Dolomedes is a diverse genus containing 105 species worldwide (World Spider Catalog, 2024). With Clerck’s (1757) descriptions of “Araneus fimbriatus Clerck, 1757 ” and “A. plantarius Clerck, 1757” the earliest taxonomic discovery of any species of Dolomedes predates Linnaeus’ system of nomenclature by a year. The genus name Dolomedes dates back to Latreille (1804) who established it for the “wolf spiders” with a second eye arrangement differing from Lycosa Latreille, 1804. According to Latreille (1804), Dolomedes was equivalent to “Les coureuses” of Walckenaer (1802), a group of spiders that contained “Araneus mirabilis Clerck, 1757 ” = Pisaura mirabilis (Clerck, 1757) and “Aranea marginata De Geer, 1778 ” = Dolomedes fimbriatus (Clerck, 1757). Although not specified in Latreille’s catalogue, it is generally believed that D. fimbriatus is the type species of Dolomedes.

Subsequent authors have described new Dolomedes species in a non-linear fashion ( Figure 4A ). Two bursts of taxonomic discovery in Dolomedes are evident, one between 1850 and 1950, and another from 2000 onwards. The leading taxonomists are Carl Friedrich Roewer (Roewer, 1955), Robert J. Raven, and Wendy Hebron (Raven and Hebron, 2018). The result of taxonomic discoveries is that Dolomedes species diversity is well documented in North America, Europe, Japan, Australia, and New Zealand, but remains poorly known in regions like Africa and Southeast Asia ( Figure 4B ). Thus, despite recent species discovery, many unknown pockets of species diversity are likely yet to be uncovered, particularly in the Old-World tropics (Yu and Kuntner, 2024). Depending on location, Dolomedes are commonly referred to as fishing or raft spiders. Herein, we use the colloquial names suggested in Yu et al. (2024), where the dolomedid family are the raft spiders, while Dolomedes specifically are called fishing spiders.

For a species-rich genus, the morphology of Dolomedes is remarkably conserved. Dolomedes has a carapace that is longer than wide ( Supplementary Figure S1A ) with the posterior half slightly higher than the eye region ( Supplementary Figure S1B ). Dolomedes have eight eyes in two rows, with the posterior eye row strongly recurved while the anterior row is straight or weakly re/procurved ( Supplementary Figure S1C ). The posterior lateral eyes are fully separated from the anterior lateral eyes ( Supplementary Figure S1C ). The abdomen of Dolomedes is oval with no modifications. Dolomedes legs are prograde and usually unmodified (but see Supplementary Figure S2 ). The fourth leg is the longest, followed by the second or the first leg while the third leg is the shortest.

Dolomedes are well known for their iconic body coloration with distinct white lateral bands, patches, or spots on carapace and/or abdomen over a dark background. This color pattern is uniform in some species (e.g., D. mizhoanus Kishida, 1936, D. hydatostella Yu and Kuntner, 2024, D. rotundus Yu and Kuntner, 2024) but can also show intraspecific variation in females (e.g., D. raptor Bösenberg and Strand, 1906, and D. horishanus Kishida, 1936) or in both sexes (e.g., D. fimbriatus, D. plantarius (Clerck, 1757), D. kalanoro Silva and Griswold, 2013, D. pegasus Tanikawa, 2012, and D. sulfureus L. Koch, 1878; Supplementary Figure S3 ) (Tanikawa, 2003, Tanikawa, 2012; Tanikawa and Miyashita, 2008; Baillie et al., 2019; Serita, 2019; Yu and Kuntner, 2024). Several species uniformly lack this typical Dolomedes coloration in both sexes (e.g., D. bedjanic Yu and Kuntner, 2024). In D. sulfureus, three coloration morphs are known ( Supplementary Figure S3 ; after Tanikawa and Miyashita, 2008). Although the function of the typical Dolomedes white lateral bands is unexplored, studies in D. raptor have linked them to foraging (Lin et al., 2015; Tso et al., 2016) (see Diet & Predation Behavior) and male mating success (Lin et al., 2015) (see Reproductive Behavior). The mechanism(s) behind Dolomedes color variation has only been studied in D. plantarius. Baillie et al. (2019) investigated the proportion of banded and non-banded offspring from 47 broods with their parents of different color phenotypes. They showed that presence/absence of white lateral bands was controlled by a single-gene system where the banded allele was dominant.

All Dolomedes species exhibit moderate female-biased sexual size dimorphism (SSD) with the ratio of female to male linear size (= SSD) between 1.00 and 1.88 (see Supplementary Table S1 ). Exceptions are D. tenebrosus Hentz, 1844, D. okefinokensis Bishop, 1924, and D. raptoroides Zhang et al., 2004 with SSD ratios 2.40, 2.46, and 2.46, respectively (Carico, 1973; Zhang et al., 2004; Silva et al., 2015). The extreme SSD (eSSD; Kuntner and Coddington, 2020) in these species may be indicative of phenotypic adaptations in males that relate to reproduction (see Reproductive Behavior).

In spiders, genital anatomy provides critical taxonomic evidence to define species boundaries (Eberhard and Huber, 2010; Foelix, 2010). However, genital anatomy is conserved across Dolomedes, providing only limited species diagnostics. As the degrees of intraspecific variation vary in different groups of Dolomedes, combinations of diagnostic characteristics change even among closely related species (Yu and Kuntner, 2024). In this section, we describe the general anatomy of female epigynum and male pedipalp partially following Sierwald’s (1989, 1990) nomenclature. However, our knowledge of the precise interactions of anatomical parts of male and female genitals is currently too preliminary to allow speculation of their precise reproductive function.

The female epigyne of Dolomedes is either round, triangular, or pentagonal, but some Australian species have lateral extensions (Raven and Hebron, 2018). The epigyne is highly sclerotized and separated into two lateral lobes by the middle field with usually two membranous windows ( Figure 5A ). The median field windows in some species (e.g., D. plantarius) merge into a larger transparent part while in others (e.g., D. scriptus Hentz, 1845) are small and indistinct. Some species from Africa (D. actaeon Pocock, 1903 and D. straeleni Roewer, 1955), Madagascar (D. kalanoro), and Australia (e.g., D. briangreenei Raven and Hebron, 2018) have one or two ventral protrusions on their median field (Roewer, 1955; Raven and Hebron, 2018; Yu and Kuntner, 2024). The margins of the median field and lateral lobes together form two longitudinal epigynal folds that posteriorly lead to the copulatory openings ( Figures 5A–C ). A looped copulatory duct inserts into a spermathecal base, which connects to a small knob-, horn-, or bulb-shaped head of spermatheca via an indistinct stem. The remainder of spermathecal bases are long, curved, or spiraled, ending with short and flat fertilization ducts ( Figures 5B–D ). Two species, D. tenebrosus and D. okefinokensis have unique epigyna (Carico and Holt, 1964) with their median fields lacking membranous windows and their copulatory openings distinctly wider ( Figure 5E ) (Carico, 1973; Sierwald, 1989). However, their vulvae nonetheless share the common Dolomedes gestalt ( Figure 5F ; see Carico, 1973; Sierwald, 1989). Considering that D. tenebrosus and D. okefinokensis are both eSSD, their unique epigynal anatomy could determine their mating behavior (Schwartz et al., 2013; see also Reproductive Behavior).

The Dolomedes male pedipalp has a U-shaped tegular ring consisting of the tegulum, its distal projection, and a membranous conductor ( Figures 6A–C ). Unlike pisaurids, Dolomedes does not have a distal tegular apophysis; instead, a round, sclerotized saddle sits at the lower center of the tegular ring and connects the tegulum and the subtegulum ( Figure 6B ). Retrolateral to the saddle sits the highly sclerotized median apophysis which can be hooked (but see D. tenebrosus and D. okefinokensis; Carico, 1973). A distal sclerotized tube of the apical division that attaches to the embolus, fulcrum, and the lateral subterminal apophysis is a dolomedid feature ( Figure 6D ; Sierwald, 1990; Yu et al., 2024). Dolomedes can be separated from other dolomedids by the embolus with one simple circular or semi-circular loop (but see D. bistylus Roewer, 1955) that neither passes the dorsal part of the palp nor extends to the tip of the cymbium (Raven and Hebron, 2018; Yu and Kuntner, 2024). Dolomedes palps feature an oval or triangular basal cymbial apophysis. Palpal tibia has a ventral and a retrolateral apophysis ( Figures 6A–C ). The former is highly conserved across the genus while the latter readily distinguishes species (but, see D. minor L. Koch, 1876: Vink and Dupérré, 2010; and D. tenebrosus: Carico, 1973). Lengths of the papal tibia and the whole palp can additionally diagnose species (Tanikawa and Miyashita, 2008; Yu and Kuntner, 2024). When expanded, the left palpal organ rotates clockwise in ventral view. In D. tenebrosus the distal sclerotized tube rotates to the position between the tibia and the retrolateral tibial apophysis during mating (Sierwald and Coddington, 1988).

Although Dolomedes has been traditionally classified in Pisauridae Simon, 1890 (World Spider Catalog, 2024), these clades are not each other’s closest relatives. Instead, Dolomedes with related Oceanian genera has now been reclassified in Dolomedidae (Yu et al., 2024). In a pre-phylogenetic argumentation, Lehtinen (1967) already proposed the use of Dolomedidae, however, the family status for the clade has not been generally accepted due to conflicting topologies (Sierwald, 1990; Griswold, 1993; Zhang et al., 2004; Santos, 2007; Wheeler et al., 2017; Piacentini and Ramírez, 2019) but has recently regained phylogenetic attention (Albo et al., 2017; Hazzi and Hormiga, 2023; Kulkarni et al., 2023). Dolomedidae is now supported through a phylogenomic analysis of over half of Dolomedes species and pisaurid genera (Yu et al., 2024). This phylogeny vastly expands the prior understanding of phylogenetic relationships among Dolomedes species that has been limited to regional analyses focused on New Zealand (Vink and Dupérré, 2010), Japan (Ono, 2002; Tanikawa, 2003, Tanikawa, 2012; Tanikawa and Miyashita, 2008), and Madagascar (Yu and Kuntner, 2024). Currently, no fossil Dolomedes are known (Wunderlich, 2008; Magalhaes et al., 2020).

Among the most well-known semi-aquatic spiders, Dolomedes species are common model organisms in many study fields (see sections below). However, incomplete and conflicting Dolomedes phylogenies (see citations above) have hampered further studying the evolution of their remarkable lifestyles and related traits until very recently. Based on the phylogenomic data of more than half of the pisaurids genera and Dolomedes species, Yu et al. (2024) investigate the evolutionary shifts of lifestyles and the presence of a capture web, as well as the morphological traits accompanying a semi-aquatic lifestyle. Their results suggest that Dolomedes and dolomedids are ancestrally semi-aquatic with several independent reversals to a terrestrial lifestyle (see also Microhabitat use and preference and Locomotion & Dispersal); and ancestrally lacking a capture web without any reversals. Yu et al. (2024) also found that Dolomedes and other semi-aquatic dolomedid and pisaurid genera have wider carapaces than the terrestrial genera but with no differences in their legs. They proposed that semi-aquatic spiders need to be large enough to break through the water surface tension to forage under water.

A reference genome is currently available only for D. plantarius (GenBank GCA_907164885.2). At 2.8 Gb, its size is among the largest sequenced arachnid genomes (reviewed in Kuntner, 2022). The complete mitochondrial genome of D. angustivirgatus Kishida, 1933 has been sequenced with gene arrangement typical of mitochondrial genomes of Entelegynae spiders (Wang et al., 2020). Ten polymorphic microsatellite DNA loci were developed for D. plantarius for use in paternity studies and for analysis of population genetics (Ji et al., 2004). The newly available subgenomic data with ultraconserved elements of Dolomedes worldwide (Yu et al., 2024) will be useful, beyond phylogenomics, in efforts to generate new sets of microsatellites (Raposo do Amaral et al., 2015).

Extant Dolomedes species are distributed globally ( Figure 2 ). It is noteworthy, however, that South America seems to lack any Dolomedes diversity (the few catalogued names are ambiguous or refer to other spider groups), making it the only major continent, in addition to Antarctica, that is thought to lack Dolomedes. Furthermore, while some species such as D. triton (Walckenaer, 1837), D. fimbriatus, and D. plantarius are widespread across continents, others such as D. orion Tanikawa, 2003 (Okinawa Island) and D. schauinslandi Simon, 1899 (Chatham Island archipelago) are narrow island endemics.

Dolomedes is a relatively distal clade on the spider tree of life (Wheeler et al., 2017; Kulkarni et al., 2023). The origin of the genus is hypothesized in the Cenozoic, between 16 and 9 (mid-Miocene) million years ago (Yu et al., 2024). This relatively recent origin of Dolomedes implies that climate oscillations in the Cenozoic (Zachos et al., 2001) may have driven its diversification. Considering that the current distribution patterns of Dolomedes include most continents, glacial cycles and land bridges might also have shaped their distribution patterns. Although the origin and the biogeographic history of Dolomedes have not been directly tested, preliminary hypotheses can be derived. Considering i) the known sister relationship with the New Caledonian Bradystichus Simon, 1884 (Wheeler et al., 2017; Piacentini and Ramírez, 2019; Kulkarni et al., 2023); ii) the monophyly of Dolomedidae containing Dolomedes and Australian relatives (Raven and Hebron, 2018; Yu et al., 2024); and iii) the highest Dolomedes contemporary species richness in East Asia, one can hypothesize that Dolomedes might have originated from either Australasia or Eastern Eurasia.

Dolomedes inhabit most freshwater-related habitats, each species preferring specific microhabitats with varying flexibility ( Figure 7 ) (Carico, 1973; Jordan et al., 1994; Tanikawa and Miyashita, 2008; Ono, 2009; Vink and Dupérré, 2010; Dickel et al., 2022; Yu and Kuntner, 2024). In regions where multiple species cohabit, they distinctly differentiate their habitat usage (Carico, 1973; Vink and Dupérré, 2010; Dickel et al., 2022). By summarizing the literature, the major differences in habitat preferences among cohabiting Dolomedes are: 1) vegetation structure near and above water bodies, 2) velocity and depth of water bodies, and 3) distance to the water bodies. Aside from picking different aquatic microhabitats, we found at least eight species that do not engage water bodies frequently and can inhabit terrestrial habitats away from water (e.g., forest understory, open bushes, or tree trunks; see Supplementary Table S1 ). These more terrestrial species are found on separate landmasses, including New Zealand (D. minor ( Figure 1C ) and D. schauinslandi: Vink and Dupérré, 2010), North America (D. tenebrosus ( Figure 1H ) and D. albineus Hentz, 1845: Carico, 1973; Guarisco, 2010), and East Asia (D. sulfureus ( Figure 1I ), D. silvicola Tanikawa and Miyashita, 2008, D. nigrimaculatus Song and Chen, 1991, and D. zatsun Tanikawa, 2003: Tanikawa, 2003; Tanikawa and Miyashita, 2008; Ono, 2009; Chae et al., 2023). These instances of terrestrial lifestyle have, according to the phylogeny, evolved independently (Yu et al., 2024).

The apparent high degree of microhabitat specialization may play a role in limiting heterospecific interactions and matings, even in regions where multiple species are common. Indeed, introgression has only been recorded once between two New Zealand species (Vink and Dupérré, 2010; Lattimore et al., 2011). Cytochrome c oxidase subunit I (COI) haplotypes clearly assignable to D. aquaticus Goyen, 1888 were present in specimens of D. minor, however, the reverse situation is unknown (Vink and Dupérré, 2010; Lattimore et al., 2011). This introgression has only been identified from the southern quarter of the South Island of New Zealand despite the two species also occurring sympatrically elsewhere. It is unknown why introgression only occurs one way in these two species and why it appears to be geographically limited, but it may have something to do with species-specific microhabitat use and/or flexibility. Studies examining microhabitat use and mating behavior in these species will surely shed light on this intriguing pattern.

As a genus well known for its semi-aquatic lifestyle, terrestrial Dolomedes species raise questions about adaptations to land versus water. Tanikawa and Miyashita (2008) compared two terrestrial species – D. sulfureus and D. silvicola – to their semi-aquatic sisters and found that the terrestrial species have relatively longer first legs. A comparative analysis over the breath of Dolomedes phylogeny, however, has rejected an overall validity of this hypothesis but instead found that semi-aquatic spiders at higher hierarchical levels are larger-bodied (Yu et al., 2024). Empirical studies that focus on hydrophobic structures, mechanisms, and behavior related to locomotion on and under water (e.g., claw tuft functional morphology, the ability to dive across species) as well as resilience to dehydration are now needed to elucidate the differences between semi-aquatic and terrestrial species.

Although there is information on the population dynamics across seasons for a few Dolomedes species (e.g., D. triton: Zimmermann and Spence, 1998), most species accounts of phenology can only be estimated according to notes on collections or from anecdotal evidence. Although Dolomedes can be found throughout the year, they are most commonly observed during the mating season. Most Dolomedes seem to be nocturnal (D. minor, D. aquaticus: Williams, 1979a; D. orion: Baba et al., 2019; D. raptor: Tso et al., 2016), however, North American and European species are active during the day (e.g. D. scriptus: Scott et al., 2016; D. fimbriatus and D. plantarius: Heldingen, 1993; Dolomedes sp.: Nyffeler and Pusey, 2014).

The reproductive season for northern hemisphere species typically spans May to October (Carico, 1973; Guarisco, 2010; Nakajo, 2024), while southern hemisphere species reproduce between September to May, peaking in December and January (Vink and Dupérré, 2010). Many species overwinter as juveniles, though adults have also been found during these months (Carico, 1973; Zimmermann and Spence, 1998; Guarisco, 2010; Nakajo, 2024; Miyashita, 1986).

Many species require one to two years of development and live for several seasons (Schmidt, 1957; Zimmermann and Spence, 1998; Nakajo, 2024). This varies not only between species, but also within species. For example, in D. sulfureus, juveniles will overwinter once or twice to reach maturity depending on hatching time. Such differences in overwintering strategy might relate to the cessation of juvenile growth under short daylight conditions (Miyashita, 1986). Maturation time can also differ between the sexes, which may relate to variation in SSD. For example, Nakajo (2024) suggests male D. raptor require a year to mature, while the much larger females may need two additional years. Sex ratios in Dolomedes can fluctuate over the season, shifting from male-biased to female-biased, likely due to mating behavior, including sexual cannibalism and spontaneous male death (Zimmermann and Spence, 1992; Schwartz et al., 2013). Furthermore, protandry, or the patterns of males maturing before females, appears common (Dolomedes tenebrosus: Schwartz et al., 2013; D. triton: Johnson, 2004, Johnson, 2005). We lack data on population sex-ratio and seasonality for most species, yet this information is crucial for understanding aspects of their biology, especially as it relates to reproduction and mating systems.

Dolomedes are known to be important to nutrient flow in riparian systems (Collier et al., 2002), through their role as predators of aquatic invertebrates and vertebrates. However, their role as prey, and therefore as nutrient transfer to higher trophic levels is poorly documented.

There are sporadic references to Dolomedes as prey to generalist predators. These include little blue heron (Egretta caerulea) (Carico, 1973), frogs (Suter, 2003; Loc-Barragán et al., 2017), fish (Figiel and Miller, 1994), owls (Lindsay and Ordish, 1964), and Parasteatoda tepidariorum cobweb spiders, documented with D. tenebrosus and D. albineus specimens in their webs (Guarisco, 2010). Dolomedes fimbriatus and D. striatus Giebel, 1869 occasionally fall prey to the purple pitcher plant (Sarracenia purpurea) when using it as a refuge and hunting ground, although even newly emerged spiderlings can avoid pitcher plant predation (Leech and Buckle, 1987; Zander, 2016). Carico (1973) suggested that sphecoid wasps hunt Dolomedes, but this predation appears rare, with only occasional instances by generalist species (Krombein, 1979; Polidori et al., 2007). Furthermore, Carico (1973) speculated that visual predators must be important to multiple Dolomedes species given their cryptic coloration which helps them blend into their respective habitats.

The New Zealand fernbird (Megalurus punctatus) is a notable predator of Dolomedes, feeding on all three mainland New Zealand species (Harris, 1986; Parker, 2002). Fernbirds partially specialize in Dolomedes, taking spiderlings from nursery webs for their nestlings and consuming adult females (Forster and Forster, 1999; Parker, 2002). Bird predation is assumed to influence habitat selection in Dolomedes triton, with higher population densities forming in habitats with more potential refuges from bird and fish predators (Jordan et al., 1994). This suggests bird predation affects the behavior and habitat selection of many Dolomedes species, driving them to remain inconspicuous. The impact of bird predation on spiders varies by spider family (Gunnarsson, 2007), presenting the need for more research on its effects on Dolomedes. Future studies should examine how bird predation influences Dolomedes microhabitat selection and activity cycles to better understand its role in shaping their behavior.

Predatory fish also indirectly affect Dolomedes. While anecdotal evidence found fish eating semi-aquatic spiders (Jordan et al., 1994), experimental evidence shows that direct effects of fish predation are limited. In experimental pools, bluegill sunfish presence reduced average D. triton body size but not population size, suggesting avoidance strategies or competition for prey (Figiel and Miller, 1994). Dolomedes triton escape behavior is ineffective against simulated trout (Oncorhynchus mykiss) attacks (Suter and Gruenwald, 2000a) implying fish predation on Dolomedes is a relatively minor evolutionary factor. Similar studies, however, are needed in other Dolomedes species.

Dolomedes have numerous defense mechanisms against predation. Touch and vibration are most important in threat detection, with vision being used only secondarily, if at all (Williams, 1979a; Suter, 2003). When under threat, Dolomedes can use their rapid locomotion to escape. Williams (1979a) found that New Zealand Dolomedes tend to escape by either submerging under water or dropping to the ground (see also Locomotion & Dispersal). However, D. dondalei Vink and Dupérré, 2010 will run onto the surface of rivers, even allowing the current to take it further downstream. This species is also more difficult to disturb, indicating it could rely more on crypsis than escape behavior (Williams, 1979a). Dolomedes triton also has specialized escape behavior against frog attack, involving leaping away from the surface of the water. This behavior was tested against two frog species under laboratory conditions, and when the Dolomedes deployed this behavior, they mostly escaped predation (Suter, 2003). The behavior is effective in the wild, as Krupa (2002) found Dolomedes make up only a small proportion of frog gut contents.

Dolomedes are also preyed upon by parasitoid pompilid wasps, as evidenced by prey records in North America, Europe, New Zealand and Eastern Russia (Richards and Hamm, 1939; Harris, 1999; Kurczewski and Edwards, 2012; Kurczewski and Kiernan, 2015; Kurczewski et al., 2017; Kochetkov and Loktionov, 2019), laboratory evidence of pompilid predation on Dolomedes in Japan (Shimizu, 1992), as well as assumed interactions in Ireland (O’Hanlon and O’Connor, 2021) and India (Rajmohana, 2017). Pompilids often rob nests of other species, leading to Dolomedes becoming prey for pompilids that do not hunt them directly (Harris, 1999). Wasps hunt Dolomedes predominantly by visual cues (Shimizu, 1992) but can also utilize their antennae to follow scent trails left by spiders (Harris, 1987; Harris, 1999), and then paralyze the spider with venom. At least one case is noted of a Dolomedes resisting capture by biting a wasp (Kurczewski and Edwards, 2012). After paralysis, the spider is dragged back to the wasp’s nest. The hydrophobic nature of Dolomedes can be used by wasps to ride them as rafts, sometimes propelling themselves along the water using their wings (Evans and Yoshimoto, 1962; Shimizu, 1992; Kurczewski and Edwards, 2012). Eggs are laid on the spider, after which Dolomedes can be large enough to sustain a wasp larva through several early instars (Harris, 1999).

Generally, Pompilidae target spiders based on their ecology, but there is also evidence of specialization on Dolomedes. In New Zealand, nests of the introduced Australian Cryptochelius australis were found to have large numbers of Dolomedes. However, there are also reports of this species preying upon Miturga and Ulidon spiders (Harris, 1999; Martin, 2012). In North America, Anoplius depressipes is a specialist on Dolomedidae and Pisauridae, predominantly targeting Dolomedes, though in some cases hunting Pisaurina mira (Kurczewski and Edwards, 2012; Kurczewski and Kiernan, 2015; Kurczewski et al., 2017). Anoplius depressipes are also adapted to walk across water and dive to capture their prey (Evans and Yoshimoto, 1962; Roble, 1985; Kurczewski and Edwards, 2012). These traits are shared with Anoplius eous, however, while laboratory data shows this species to specialize on Dolomedes, it seems to hunt Pardosa pseudoannulata (Lycosidae) in the wild (Iwata, 1939; Shimizu, 1992). Details of pompilid predation and other predation on Dolomedes can be found in Table 1 .

Mantis lacewings (Mantispidae) are also spider-specific parasitoids (Kaston, 1938). Unlike the above-mentioned wasps, mantispid larvae target spider eggs by “hitchhiking” on spiders then entering their egg sacs when the female spiders are laying eggs (Haug et al., 2018). So far, direct record of Mantispidae parasitizing Dolomedes is only known from a female D. bedjanic from Madagascar, where Yu and Kuntner (2024) found a mantispid larva in the spider’s epigastric furrow.

Despite their ecological importance, spiders are rarely the focus of conservation programmes (Milano et al., 2021) but wetlands, where many Dolomedes are located, are estimated to have decreased between 33% and 87% since the 18^th Century (Davidson, 2014; Hu et al., 2017). Wetlands provide vital ecological services, including temperature regulation, pollution filtering, and surface runoff control (Zedler and Kercher, 2005). Unfortunately, these vital habitats face significant degradation from urbanization, agriculture, pollution, and climate change (Davidson, 2014; Hu et al., 2017). Monitoring organisms like spiders can help gauge the impact of human activities on these crucial habitats.

Two species of Dolomedes are of current conservation interest; D. plantarius from Europe and D. schauinslandi from the Chatham Islands of New Zealand. The former is rated as “vulnerable” on the IUCN Red List (World Conservation Monitoring Centre, 1996) while the latter is classified as “At Risk: Relict” in New Zealand (Sirvid et al., 2021).

Dolomedes plantarius is one of the most widespread Dolomedes species, distributed from Siberia to Britain and from the Apennines to Scandinavia (World Spider Catalog, 2024). However, the species prefers very specific habitats which are in general well-vegetated open water bodies with low velocity (Dickel et al., 2022), such as lowland rivers, bogs, fens, and oxbows (Smith, 2000; Van Helsdingen, 2005; Duffey, 2012). Dolomedes plantarius is considered threatened by habitat loss and degradation caused by human activities (Smith, 2000; Duffey, 2012; Milano et al., 2021). Although our knowledge of their distribution ranges remains largely incomplete, recent estimations and modeling of their suitable habitats (Leroy et al., 2013, Leroy et al., 2014; Monsimet et al., 2020; Milano et al., 2022) show that D. plantarius is under more pressure from climate and land use changes than D. fimbriatus. Compared to D. fimbriatus, D. plantarius exhibits narrower habitat preferences as well as poorer ability of both waterborne and airborne long-distance dispersal (Monsimet et al., 2020, Monsimet et al., 2022; see also Locomotion & Dispersal). Overall, the distribution ranges of D. plantarius are estimated to decrease and shift northward following the trends of global temperature rising (Leroy et al., 2013, Leroy et al., 2014; Monsimet et al., 2020; Milano et al., 2022).

Dolomedes plantarius is listed in the national Red Lists of 13 European countries with nine of them protecting the species and its habitats by law (see Milano et al., 2021). The United Kingdom (UK) is the only country that applies further actions in protecting D. plantarius (Smith, 1996, Smith, 2000, Smith, 2005 ¹ ; Duffey, 2012; Smith et al., 2013). There are only three disjunct natural populations of D. plantairus left in the UK (Duffey, 2012). Therefore, the species is suggested to be highly vulnerable with urgent need of conservation action to prevent local extinction. Habitat restoration work and regular census of D. plantarius at Lopham Fen National Nature Reserve has occurred since 1991 to prevent degradation of current water bodies and create new habitats (Smith, 1996, Smith, 2000, Smith, 2005 ¹ ). Although long-term monitoring suggests that the population sizes of D. plantarius vary drastically across years, progressive vegetation restoration at the site has allowed considerable expansion of the population over the last decade (Smith, 2005 ¹ ; Smith, 2020). In addition, the conservation framework of D. plantarius in the UK also includes translocation. Starting in 2010, Smith et al. (2013) launched the translocation project of D. plantarius aiming to expand its populations from three to 12 in the UK following the IUCN protocols. By 2021, the translocation project had successfully increased the D. plantarius populations from three to seven (Milano et al., 2021).

Unlike D. plantarius, the degradation of wetlands does not explain the decline of D. schauinslandi, found in forest and scrublands away from waterways on three small islands in the Chatham Island archipelago (Hokorereoro/Rangatira/South East, Maung’Re/Mangere, and Houruakopara) in New Zealand. It was previously found on Rangihaute/Rangiauria/Pitt Island before going extinct in the early 1900s (Vink and Dupérré, 2010) and was likely also found on Rēkohu/Wharekauri/Chatham Island. Despite being a threatened species, little is known about its biology, making it an obvious subject for conservation genomics and ecology research. In particular, understanding the interacting effects of dispersal behavior, impacts of invasive predators, habitat availability and quality, prey availability, and climate change are essential for the future of this species.

It is unlikely that these two species are the only Dolomedes affected by global change, but understanding the impacts of anthropogenic pressures is difficult when we lack diagnosis of threat status for most species. A relatively new research avenue involves studying the effects of heavy metals and pharmaceuticals on aquatic spiders as bioindicators of waterway pollutants. For example, Ortega-Rodriguez et al. (2019) found that an unidentified Dolomedes had the highest methylmercury concentration among numerous shoreline spiders, likely reflecting their aquatic prey diet. Given their close proximity to water and ease of observation, using Dolomedes as bioindicators of a range of anthropogenic impacts provides a fruitful avenue for future research.

Given that many Dolomedes species hunt on water, a strong focus of their sensory physiology has been the detection of waterborne prey. Prey detection and stimulus discrimination has been well-investigated in D. triton (Bleckmann and Barth, 1984; Bleckmann and Rovner, 1984; Bleckmann and Bender, 1987; Bleckmann and Lotz, 1987; Bleckmann et al., 1994; Suter, 2003) as well as in D. okefinokensis (Bleckmann et al., 1994). Dolomedes can locate prey using different environmental cues, with artificially generated water surface waves showing the highest spider responsiveness, followed by airborne vibrations (Bleckmann and Rovner, 1984; Bleckmann and Barth, 1984). Notably, visual stimuli were shown to trigger spider reactions in a few cases as well (Bleckmann and Rovner, 1984).

Dolomedes are likely to detect water surface waves using lyriform organs (a slit organ on the metatarsus of the legs; Figure 8A ) and airborne vibrations using trichobothria (long, thick sensilla; Figure 8B ). Studies have shown that spiders are attracted to stimuli with an irregular mix of low and high frequencies, including those about 30–40 Hz (Bleckmann and Barth, 1984; Bleckmann and Lotz, 1987). In comparison, wind generated surface waves rarely exceed 10 Hz (Bleckmann and Rovner, 1984). Sensory abilities and reactions to wave sources also seem to differ between species, as shown in a comparative study on D. fimbriatus and D. triton (Bleckmann and Barth, 1984). Dolomedes fimbriatus has a larger error angle (i.e., the spider is less accurate in targeting the wave source) and is slower than D. triton (Bleckmann and Barth, 1984). Both the lyriform organ and trichobothria were shown to be crucial to minimize the error angle when spiders move towards or escape from a wave source (Bleckmann and Rovner, 1984; Suter, 2003). The morphology and ultrastructure of Dolomedes sensory structures is only briefly touched on by a few studies. For New Zealand species mechanoreceptive sensilla and contact-chemoreceptors have been discussed (Williams, 1979a), but never described in further detail. There is much room for comparative studies on sensory systems across Dolomedes, especially focused on terrestrial versus water-associated species.

Dolomedes, like the majority of spider groups, are thought to have rather poor vision. Nonetheless, Dolomedes use visual cues during predation and presumably also during courtship (Roland and Rovner, 1983; Bleckmann and Barth, 1984). Dolomedes triton, for example, was found to run slower and shorter distances towards prey when blinded (Bleckmann and Barth, 1984). They also appear able to focus light under water, because the surrounding body hairs capture a thin air layer (Williams, 1979a). However, the extent to which they might use vision underwater, and whether this varies across species, has yet to be explored.

There are detailed descriptions of the architecture of the eyes of D. aquaticus and other New Zealand Dolomedes species (Blest and Day, 1978; Williams, 1979b) as well as the tapetum lucidum (a light-reflecting layer inside the eye) of D. tenebrosus, D. triton, D. scriptus and D. vittatus Walckenaer, 1837 (Benson and Suter, 2013). But apart from those studies, there has been little work done on the anatomy of the visual system. To our knowledge, no studies have explored the processing pathways of the primary and/or secondary eyes of any Dolomedes species. Such a study would be interesting, as major differences were recently discovered in the central nervous system of primarily web building versus cursorial spiders. While cursorial species possess prominent higher order processing centers (mushroom bodies) and visual neuropils, web builders have those regions reduced or absent, however their leg neuropils are proportionally larger (Steinhoff et al., 2023). We would predict Dolomedes central nervous system patterns to be like those described in other cursorial species, but detailed neuroanatomical studies are needed.

Given their often-close connection with water, Dolomedes are highly capable of moving across its surface ( Figure 9A ). Early research explored their patterns of locomotion across terrestrial versus water surfaces (multiple species: Ehlers, 1939; D. fimbriatus: Barnes and Barth, 1991; D. triton: Shultz, 1987) and comparative studies suggest that Dolomedes are specialized for water locomotion (Shultz, 1987; Barnes and Barth, 1991; Stratton et al., 2004).

Two types of water surface gaits have been described – rowing (D. triton: McAlister, 1960; Shultz, 1987; D. plantarius: Gorb and Barth, 1994; Suter and Gruenwald, 2000a, Suter and Gruenwald, 2000b) and galloping or running ( Figure 9B ; D. triton: Suter and Wildman, 1999; D. plantarius: Gorb and Barth, 1994); the latter of which tends to be associated with prey capture (D. plantarius: Gorb and Barth, 1994). Rowing Dolomedes can reach speeds of <0.27m/s (reviewed in Suter, 1999) and involves the use of leg pairs II and III in synchrony while legs I and IV are motionless and held parallel to the direction of movement. Galloping is much faster, with individuals moving more than 0.4m/s,and involves leg pairs I, II, and III moved in synchrony (reviewed in Stratton et al., 2004). Numerous studies have explored the posture, gait, and rowing behavior of Dolomedes on different substrates and/or on water with different viscosity and depth (e.g., D. aquaticus: Campbell et al., 2014; D. triton: Shultz, 1987; D. fimbriatus: Barnes and Barth, 1991) while others have explored their hydrophobicity and escape responses across water (D. aquaticus and D. minor: Williams, 1979a).

In 2004, Stratton and colleagues greatly expanded our understanding of spider locomotion on water by conducting a comparative study exploring water-surface locomotion from 249 spider species across 42 families. Trechaleidae Simon, 1890 and Pisauridae (at the time, containing Dolomedes) were the only focal families to show a monomorphy for both a hydrophobic surface (remaining dry and completely above the water surface) and movement by rowing. All five Dolomedes species tested (D. albineus, D. tenebrosus, D. triton, D. gertschi Carico, 1973, and D. vittatus) demonstrated rowing and the genus was used as the standard against which other species were compared (Stratton et al., 2004). A specialized rowing gait was hypothesized to have evolved at least 4 times independently, with hydrophobicity suggested to be a preadaptation to aquatic gaits. Rowing behavior, however, was hypothesized to have evolved once at the base of the clade that includes Pisauridae (containing Dolomedes), Lycosidae and Trechaleidae. The specialized gait of pisaurids is facilitated by dimple distortion, drag, generation of vortices, and the hydrophpilic hairs (Suter, 2013). The results of Stratton et al. (2004) aligned with the latest study (Yu et al., 2024) suggesting that the semi-aquatic lifestyle is ancestral to Dolomedidae, Pisauridae, Lycosidae, and Trechaleidae. Considering our knowledge of the aquatic movement patterns is limited to a few Dolomedes species, an expanded investigation across a broader range of Dolomedes species would allow a more nuanced understanding of the evolution of water-surface locomotory gaits and associated traits.

Dolomedes triton has also been observed “sailing” by extending and elevating its anterior pair of legs and letting the wind carry it across the water’s surface (Deshefy, 1981). Another distinct form of sailing involves the spider lifting its body above the water surface by extending and depressing all of its legs (Suter, 1999). Controlled studies of this elevated posture reveal that it is a cheap form of locomotion but comes at the cost of reduced control of directionality (Suter, 1999). Expanding biomechanical and behavioral studies of sailing to other Dolomedes species, potentially with a focus on locomotion across distinct bodies of water (e.g., fast flowing versus stagnant) could provide information regarding the evolution of mechanisms of unique locomotion.

In addition to moving across water, many Dolomedes species can submerge underwater ( Figures 9C, D ) in response to predation risk, by exploiting air bubbles created by hydrophobic hairs spread across their body. Submergence tests revealed that D. triton individuals would dive under water and remain there voluntarily from 4–30 minutes, with at least one individual remaining responsive underwater for more than 3 hours (McAlister, 1960). Similarly, D. aquaticus can stay submerged for up to 30 minutes (Forster and Forster, 1973). Dolomedes triton appeared to require solid support structures to break through the water surface both on entry and exit (McAlister, 1960; Williams, 1979b) and similar observations of the requirement of a substrate for submergence were seen in New Zealand’s Dolomedes (presumably D. minor, D. aquaticus, and D. dondalei: Williams, 1979a). Interestingly, McAlister noted that D. vitattus (referred to as D. urinator Hentz, 1845) exhibits a different exit behavior (McAlister, 1960), which sounds similar to some of the feeding positions of D. dondalei (Williams, 1979a) – remaining largely submerged with one or two legs protruding above the water. Given observations of distinct exit behavior, comparative work across species exploring the biomechanics of submergence and re-emergence might provide insights into the evolution of related morphologies – e.g., size variation.

To disperse, spiders can actively walk over short-distances or passively travel over longer-distances by ballooning, like many spiderlings do after their first molts in their nursery web (Bell et al., 2005; Vink and Dupérré, 2010; Frost et al., 2013; Monsimet et al., 2022). Species-level differences have been found too: for example, Dolomedes fimbriatus, a species with less habitat specialization, demonstrated a higher propensity for long-distance dispersal (both airborne and waterborne), while the more habitat specialized D. plantarius was more likely to engage in waterborne rowing (Monsimet et al., 2022). In the field, quantified distances of dispersal are lacking for any species. Studies aimed at Dolomedes dispersal distance and patterns could provide insight into the likelihood of establishment for species of conservation concern, such as D. plantarius and D. schauinslandi, in newly restored habitats or for translocation. Such studies could also inform hypotheses about the global distribution of Dolomedes.

Little is known about individual movement patterns in most Dolomedes species. In D. triton, a field survey using marked individuals found that adult females moved more than juveniles, but their movement reduced again once they produced egg sacs (Kreiter and Wise, 1996). This increase in movement with adulthood was presumed to be associated with more active, versus passive, hunting in adult females, but could also relate to distinct age or size-related predation pressure. To fully understand the natural history of Dolomedes, we require additional information on species-specific movement and dispersal patterns.

Like most spiders, Dolomedes are opportunistic predators with broad diets ( Figure 10 ), although invertebrates seem to make up most of their catch ( Figures 10A, B ). In D. triton, semi-aquatic and aquatic insects and spiders form most of their diet, dominated by Hemiptera, Odonata and Diptera (Zimmermann and Spence, 1989). Similarly, D. dondalei and D. aquaticus primarily consume aquatic insects, especially Diptera (mostly tipulids), Trichoptera and Ephemeroptera. An isotope analysis confirmed that aquatic insects are a key component of Dolomedes diet, although this varied between sites (Collier et al., 2002). Cannibalism can also form a significant portion of Dolomedes diet ( Figure 10C ; e.g. Greenwood et al., 2010). For example, in D. triton conspecifics formed about 5% of their diet (Zimmermann and Spence, 1989). The diet of terrestrial Dolomedes species (e.g. D. schauinslandi; Figure 10A ) is less known, but presumably comprises of terrestrial invertebrates. Even in semiaquatic species, small juveniles may forage on vegetation away from the water that larger juveniles and adults rely on (Zimmermann and Spence, 1998). The extent to which Dolomedes feed on aquatic versus terrestrial prey may be important in their roles as bioindicators as well as in their susceptibility to distinct forms of environmental contamination.

Dolomedes do not limit their diet to small invertebrates, capturing the attention of biologists and arachnophobes alike with their predation of vertebrates, including fish ( Figure 10D ; Williams, 1979a; Nyffeler and Pusey, 2014), lizards (Eversole, 2022), amphibians (frogs, tadpoles, toads, and newts; Figure 10E ; Moore and Townsend, 1998; Cabrera-Guzmán et al., 2015), bats (Leivers et al., 2021), as well as large freshwater crustaceans ( Figure 10F ; Kosuge and Sasaki, 2002; Baba et al., 2019). A review by Nyffeler and Pusey (2014) reports observations of fish predation in the wild across 11 Dolomedes species. It seems appropriate to refer to Dolomedes as fishing spiders given widespread fish predation in the genus.

Adult Dolomedes spiders forego capture webs, opting instead to position themselves motionless to sit and wait for their prey to walk or float by. A characteristic behavior of semi-aquatic Dolomedes is to dangle their anterior legs over water surfaces in anticipation of prey floating past (Williams, 1979a). They will pursue prey, but only after initial detection (Williams, 1979a) and they do not actively hunt throughout the landscape, in contrast to roaming predators. Dolomedes use their chelicerae to inject venom, which immobilizes and kills prey, followed by extraintestinal digestion, some species transport prey to land after capture (Forster and Forster, 1973; Williams, 1979a; Uzenbaev and Lyabzina, 2009). Meal completion in D. minor can range from 10 to 30 minutes from prey capture, depending on prey size (Forster and Forster, 1973).

The use of body coloration in prey capture has also been suggested to help Dolomedes forage. For example, female D. raptor use distinct white patches of hairs on their legs to lure prey (Tso et al., 2016), while bright white stripes on male cephalothorax provide a similar function for prey attraction (Lin et al., 2015). Several other Dolomedes similarly possess such distinct leg patches in females (e.g. D. horishanus and D. hydatostella) or cephalothorax stripes in males (e.g. D. fimbriatus, D. rotundus), with related species lacking them, offering a valuable system to determine the prevalence of luring and compare prey capture techniques in this group.

Given that Dolomedes are able to take down vertebrates that can be many times larger than the spider itself, there has been significant interest in the function and biochemical properties of the venom for a handful of species – D. fimbriatus (Uzenbaev and Lyabzina, 2009; Kozlov et al., 2014) D. mizhoanus (Jiang et al., 2013; Li et al., 2014; Xu et al., 2015), D. sulfureus (Wang et al., 2013; Xu et al., 2015), and D. okefinokensis (McCormick et al., 1993; Meinwaldt and Eisnert, 1995). Bioactivity assays have shown that Dolomedes venom has a neurotoxic effect, causing disorientation, altered movement, and ultimately the death of prey (Li et al., 2014). Venoms of several Dolomedes species have been analyzed using mass spectrometry (McCormick et al., 1993; Meinwaldt and Eisnert, 1995; Wang et al., 2013; Li et al., 2014) and transcriptomics (Kozlov et al., 2014; Xu et al., 2015; Jiang et al., 2013). These studies document the diversity and structure of venom polypeptides, aid in reconstructing the evolutionary history of spider venom, and contribute to our understanding of venom function. Dolomedes venom seems to be of special interest in the potential for neurochemical and neurotherapeutic drug development, particularly because they can prey upon vertebrates, which suggests their venom contains neurotoxins that are targeted for vertebrate nervous systems (Li et al., 2014).

Dolomedes courtship behavior ( Figure 11A ) has received less attention compared to other spider groups that show conspicuous behavior (see for a review: Huber, 2005) – e.g., the numerous colorful jumping spiders that engage in complex dances (reviews: Richman and Jackson, 1992; Elias et al., 2012; Nelson, 2023) or wolf spiders like the genus Schizocosa Chamberlin, 1904 which have conspicuous ornaments combined with complex songs and dances and whose study has contributed significantly to our understanding of complex multimodal signaling (Starrett et al., 2022 and references therein). Dolomedes lack obvious secondary sexual traits, sensational courtship or extensive silk use during courtship, all traits which have been observed in other spider taxa (e.g., some nephilids (Zhang et al., 2011) and pisaurids (Anderson and Hebets, 2016) (reviewed in Scott et al., 2018). As such, there has been little research on the relationship(s) between reproductive behavior such as courtship and mating success in Dolomedes.

Early studies on D. scriptus and D. triton showed that female silk contains sex pheromones, which aid as chemical cues for males who follow female draglines (Kaston, 1936; Roland and Rovner, 1983), inducing courtship displays. These pheromones are probably emitted from the female’s integument to the surrounding water, which may help males locate potential mating partners (Roland and Rovner, 1983). The species-specificity of pheromones and/or the potential for airborne signals/cues remain unexplored in Dolomedes.

Though courtship behavior likely varies in intensity, duration and specific expression between species, all investigated species share common features. The first phase of male courtship usually includes a series of leg movements (visual and vibratory modalities), which are often referred to as “leg-waving”, “tapping” and “jerking” (Kralj-Fišer et al., 2016). Next, males touch the female on their legs and abdomen (Carico, 1973; Roland and Rovner, 1983; Sierwald and Coddington, 1988; Arnqvist, 1992; Lin et al., 2015). In D. fimbriatus, male courtship was found to vary with female traits – females with lower body weight received less intense male courtship and were more likely to remain unmated (Kralj-Fišer et al., 2016). To date, however, no information exists regarding the relationship between courtship duration and/or complexity and male mating success. Male coloration appears to play a significant role in female mating decisions. For instance, in D. raptor, females are more likely to reject and even attack males that lack the species-typical white stripes (Lin et al., 2015). Female mate choice based on other visual or vibratory cues/signals has not received much attention in other Dolomedes, but they are worth investigating further, especially in conjunction with studies on their sensory ecology and physiology.

Female responses to courting males are quite variable among species. In D. scriptus and D. triton, females may respond to courting males with their own courtship behavior, such as “drumming” and “leg waving” (Roland and Rovner, 1983; Schoenberg et al., 2022), while females of D. fimbriatus react either by attacking the male or staying motionless in a receptive body position (Arnqvist, 1992), similar to the motionless female D. tenebrosus (Sierwald and Coddington, 1988). Males mount females usually facing the opposite direction and start inserting their pedipalps for sperm transfer (Sierwald and Coddington, 1988; Arnqvist, 1992; Schoenberg et al., 2022). The motionless state of females is reminiscent of the quiescence described in other spiders (reviewed in Cargnelutti et al., 2023) and would be interesting to explore further.

The duration of copulation as well as the number of pedipalps used for insertions varies across Dolomedes species. Copulation duration (male mounting female and inserting pedipalp/s) can be rather short (e.g., a few seconds in D. vittatus, D. triton, and D. fimbriatus: Carico, 1973; Arnqvist, 1992) or relatively long (on average 22 minutes in D. tenebrosus: Schwartz et al., 2014; though most of this time involves the male’s body hanging from the female as his heart slowly stops beating). The pattern of pedipalp use (one or both) varies between but also within species (Schmidt, 1957; Carico, 1973; Johnson, 2001; Schoenberg et al., 2022; Sierwald and Coddington, 1988; Arnqvist, 1992; Schwartz et al., 2013). Quantifying the relationship between copulation duration, number of pedipalps being used and sperm transfer, as well as disentangling the roles of each sex in copulation duration, will help us understand the observed variation and the potential role of sexual selection and sperm competition in influencing these evolutionary patterns.

In Dolomedes we observe great variation in species-specific patterns of female and male mating rates (i.e. mating systems; Table 2 ). At one extreme end of the spectrum we find D. tenebrosus, a species in which females will mate with up to three males while males will die in 100% of first matings (spontaneous male death; Figure 11B ), making them strictly monogynous (Schwartz et al., 2013, Schwartz et al., 2014). At the other end of the spectrum, D. fimbriatus, D. scriptus and D. triton males mate with multiple females, making them polygynous (Arnqvist and Henriksson, 1997; Johnson, 2001; Kralj-Fišer et al., 2016; Schoenberg et al., 2022). Since both sexes have paired genitalia, males can potentially inseminate the same female twice, inserting both pedipalps in different openings. There is also evidence of high individual variation within the same population in a female’s number of mates (Arnqvist and Henriksson, 1997; Johnson, 2001; Kralj-Fišer et al., 2016; Schoenberg et al., 2022). Details of mating and cannibalism rates for previously studied species are summarized in Table 2 .

The spontaneous death by male D. tenebrosus provides an intriguing example of monogyny (including terminal investment strategies) (for examples from other spiders and social insects see: Boomsma et al., 2005; Schneider and Fromhage, 2010; Jaffé et al., 2014) and provides a system in which to test hypotheses of the evolution of this mating system. In D. tenebrosus, the male’s death coincides with his consumption by the female, which has been shown to benefit both sexes through higher offspring quantity and quality (Schwartz et al., 2016). Various life history traits linked to monogyny are also observed in D. tenebrosus – i.e., a male-biased sex ratio and eSSD (Fromhage et al., 2007; Miller, 2007; Wilder and Rypstra, 2008; Schwartz et al., 2013). To fully leverage Dolomedes mating system evolution, more data on the mating systems and life history traits of additional species is needed for comparative analyses. Research on D. scriptus (Schoenberg et al., 2022), D. tenebrosus (Schwartz et al., 2013, Schwartz et al., 2014) and D. triton (Wojcicki, 1992) provide a good start, but such a diverse genus offers a wealth of further species to contribute to a comprehensive comparative study.

Female aggression, often resulting in precopulatory and postcopulatory sexual cannibalism (consuming a mate before, during or after copulation; reviewed in Burke, 2024), is present in many Dolomedes species and significantly impacts mating rates and population dynamics (D. fimbriatus: Arnqvist, 1992; D. triton: Johnson, 2005b; Johnson and Sih, 2005; D. scriptus: Fisher and Price, 2019; Schoenberg et al., 2022). Numerous hypotheses have been proposed to explain sexual cannibalism ( Figures 10C , 11C ; reviewed in Burke, 2024), and a few have been tested with Dolomedes. Using D. fimbriatus, for example, Arnqvist and Henriksson (1997) found no evidence for Newman and Elgar (1991) idea that pre-copulatory sexual cannibalism represents a female’s assessment of a male’s value as a sperm donor versus a prey item, as female foraging history did not influence likelihood of cannibalism. An alternative hypothesis – the “aggressive spillover hypothesis” – was discussed in the same publication by Arnqvist and Henriksson (1997). They proposed that high female aggression towards males may stem from selection for a general predatory aggressive syndrome that is beneficial in a foraging context but potentially costly in a mating context. The aggressive spillover hypothesis has been tested in two Dolomedes species that showed mixed results. While a study on D. fimbriatus did not find evidence of a correlation between female foraging aggression and aggression toward courting males (Kralj-Fišer et al., 2016), a study on D. triton showed that foraging aggression was positively correlated with increased sexual cannibalism, feeding rate, larger adult size, boldness towards a threat and higher fecundity (Johnson and Sih, 2005). Further research exploring relationships between aggression and reproductive behavior are necessary to discern the potential role of female aggression in influencing reproductive strategies across Dolomedes and the potential for sexual cannibalism to be a sexually selected trait (Burke, 2024).

There are also interesting first insights into the existence of consistent among-individual differences in aggressiveness (i.e. “personality” traits) in Dolomedes and their correlation to sexual behaviors. In D. fimbriatus, for example, female voracity towards prey might be considered an intrinsic personality trait, but not aggression towards mates, as females adjusted their aggressive responses towards courting males based on the male’s size relative to their own (Kralj-Fišer et al., 2016). In contrast, D. triton female aggression levels were consistent across contexts, with D. triton females showing positive behavioral correlations between foraging voracity, sexual cannibalism tendency, and boldness in response to predation risk (Johnson and Sih, 2005, Johnson and Sih, 2007). Given the heightened interest in animal personality and behavioral syndromes in the last decades (see for example: Réale et al., 2007; Sih et al., 2015; MacKinlay and Shaw, 2023), Dolomedes could be a useful taxon to address questions related to the extent to which certain behavior is fixed per individual (i.e., a personal trait) or context dependent.

Previous experience also influences cannibalistic behavior in Dolomedes. Specifically, works on D. triton, D. scriptus, and D. fimbriatus found females to be significantly more aggressive to courting males if already mated (Zimmermann and Spence, 1989, Zimmermann and Spence, 1992; Johnson, 2001; Kralj-Fišer et al., 2016; Schoenberg et al., 2022). In D. triton, females that cohabited with adult males were more likely to subsequently cannibalize males during courtship encounters later in life (Johnson, 2004). Furthermore, levels of SSD also impact the probability of a female cannibalizing a male – i.e., when size differences were minimal, male D. fimbriatus and D. triton had a higher chance of evading female attacks (Johnson, 2005; Johnson and Sih, 2005; Kralj-Fišer et al., 2016). These latter results are consistent with the idea that female aggression towards males is non-selective with cannibalism being contingent upon the female’s physical power relative to the male’s defensive capability (Wilder and Rypstra, 2008; Roggenbuck et al., 2011).

In contrast to pre-copulatory sexual cannibalism, post-copulatory sexual cannibalism occurs after sperm transfer, making it possible for males to receive a fitness benefit from being cannibalized. Such a benefit was observed for both sexes in D. tenebrosus as females that cannibalized males after copulation produced more offspring that were higher in mass and survived longer than the offspring of females who consumed a similarly sized cricket (Schwartz et al., 2016). To date, it is unknown whether this benefit is specific to the consumption of male D. tenebrosus, or simply to the consumption of a new prey type. It is also unknown whether similar fitness benefits are present from post-copulatory sexual cannibalism in other Dolomedes species. Dolomedes tenebrosus is an eSSD species and has received attention because the male’s terminal investment strategy of obligate death following sperm transfer makes the males complicit in their own cannibalism (Schwartz et al., 2013, Schwartz et al., 2014). Complicity in sexual cannibalism has not yet been observed in other Dolomedes species. It remains unclear what, if any, mechanisms of post-copulatory sexual selection are at play in this system, but future studies exploring the potential for sperm competition and cryptic female choice are likely to reveal interesting patterns across species.

Dolomedes parental care is strictly maternal. Upon oviposition, female Dolomedes create a silken egg sac, holding it tight in their chelicerae, with their pedipalps extended over the front, and a silk dragline attached to their spinnerets ( Figures 11D, E ; Comstock, 1912). The egg sacs of D. triton have a unique, highly hydrophobic outer layer, allowing them to submerge their egg sacs (Correa-Garhwal et al., 2019). The egg sac exudes a buoyant force while submerged, resulting in the female exerting more pressure to remain underwater (McAlister, 1960), away from potential threats. Egg sacs are highly protected by the female and difficult to remove without tearing the lining of the egg sac (Johnson and Sih, 2007). Even unmated females have been observed guarding unfertilized egg sacs, however unfertilized egg sacks are also frequently consumed (Schmidt, 1957; Arnqvist, 1992; Fisher and Price, 2019). The only time a female will let go of her egg sac is to forage, after which she will resume carrying the egg sac (Forster and Forster, 1973). A study by Johnson and Sih (2007) found a significant negative correlation between a female’s boldness in guarding her egg sac and her body condition, denoting the importance of foraging to the cost of parental care. As with most topics discussed thus far, data on parental investment come from only a handful of species, leaving open the possibility of variation across the genus in parental investment.

A general timeline of reproduction for some common Dolomedes species is within Table 3 . Female Dolomedes will travel with their egg sacs until close to hatching (Comstock, 1912). Spiderlings hatch within the egg sac as they are being carried (Forster and Forster, 1973). Near the time of the spiderlings’ first molt, the female constructs her nursery web and deposits the egg sac (Carico, 1973; Forster and Forster, 1973; Vink and Dupérré, 2010). She will tear open the egg sac using her chelicerae, releasing her offspring into the nursery web ( Figures 11F–H ; Comstock, 1912; Nicholas et al., 2011). In New Zealand, nursery webs of D. minor are more easily seen than the spiders. These distinctive nursery webs appear as little white purses, often on the tips of shrubs (Forster and Forster, 1973). On the other hand, in some species like D. fimbriatus nursery webs are less distinct, being made of sparser silk ( Figure 11G ) and persist for a shorter time. The placement of nursery webs by some female Dolomedes is purposeful and habitat specific. A study by Kreiter and Wise (1996) found a preference for placing nursery webs in Juncus effusus and structurally similar Juncus-like vegetation. Similarly, Dickel et al. (2022) found that D. plantarius showed a strong association with Carex sp. and that distance to water was a significant factor of web placement.

Parental care in Dolomedes does not end at hatching, as females are infamous for fiercely guarding their young. If a threat approaches the nursery web, the female will aggressively approach and may be prompted to bite (Comstock, 1912). Much of the research on female aggression has addressed its benefits to female fecundity, but no studies have investigated the benefits of female aggression to offspring survival post-hatching.

We uncovered numerous avenues for further investigation regarding the systematics and morphology of Dolomedes. The recent placement of Dolomedes within the newly resurrected Dolomedidae family (Yu et al., 2024) marks a significant advancement in our understanding of their systematics, but many questions remain. Prioritizing the phylogenetic testing of the monophyly and the nomenclatural validity of Dolomedidae with increased taxon sampling is essential, along with clarifying their biogeographic history. If Miocene climatic oscillations have shaped their trait evolution and diversification, then Dolomedes can inform us of future biotic responses to global change. Expanding taxonomic descriptions to understudied regions (central Africa, Madagascar, India, Southeast Asia, and Oceania) is crucial for a more balanced understanding of their diversity. Further taxonomic discoveries will facilitate reconstruction of a more complete species-level phylogeny, strengthening evolutionary analyses, classification decisions and biogeographic reconstruction. Furthermore, the few South American Dolomedes are likely misplaced, leaving a continent curiously devoid of these almost globally distributed creatures – a biogeographic puzzle possibly explained by competition from earlier-arriving, semi-aquatic spiders.

We identified several unknowns regarding Dolomedes morphology. One key question is the adaptive function of color pattern variation within and among species. A comparative study mapping the occurrence of white lateral bands and their functions across species would provide valuable insights into the selective pressures driving and maintaining this variation. Studies on D. raptor suggest these bands play roles in both foraging and mate choice (Lin et al., 2015; Tso et al., 2016), but the extent to which this applies to other species is unknown. Furthermore, studies incorporating within-species variation would be powerful for untangling proximate and ultimate causes of polymorphism in body color patterns. Another set of morphological questions concerns the functional implications of divergent genital morphology in species, such as D. tenebrosus and D. okefinokensis, which also exhibit other traits such as eSSD and unusual mating systems. We suspect that this variation is driven by sexual conflict over mating optima, including gametic competition and choice, and look forward to future studies exploring these possibilities.

The ecology of Dolomedes offers opportunities for insight into the interface between aquatic and terrestrial ecosystems and associated adaptations. Apparent microhabitat specialization coincident with indications of recent divergence (Yu et al., 2024) suggests that microhabitat specificity may have influenced diversification in Dolomedes; a hypothesis that requires testing. Numerous opportunities also exist to explore potential adaptations to aquatic versus terrestrial lifestyles, especially studies that focus on populations that vary in their aquatic/terrestrial lifestyle and/or species that change their microhabitat use throughout their life.

Often found at the boundary between freshwater and terrestrial ecosystems, Dolomedes are ideal for testing the effects of anthropogenic pressures on behavior, ecology and morphology. Early evidence suggests Dolomedes can serve as bioindicators of heavy metals in waterways (Ortega-Rodriguez et al., 2019) but there is significant potential to explore the impacts of a wider range of pollutants, including agrichemicals, pharmaceuticals and excess nutrients, on these key ecosystem predators and their prey. Additionally, many Dolomedes are found along urban-rural gradients, offering a natural transect to tease apart the pollutant impacts. Furthermore, the effects of global change on the behavioral ecology of animals are a rapidly growing area of research (Wong and Candolin, 2015). One area of interest has been the effect of pollutants on aquatic animal behavior, especially signaling and communication (reviewed in Saaristo et al., 2018). Although Dolomedes have yet to be studied from this perspective, observable courtship and reproductive behavior make them ideal candidates. They would also be a good taxon to explore for targeted citizen science data projects, like iNaturalist, for documenting distributions and diets (see Powell et al., 2021).

Seasonal variation in maturation times and sex ratios across Dolomedes makes them a potential model system for exploring the relationship between life history and reproductive traits. Sex ratios, for example, are theoretically and empirically linked to SSD across animals and often, to extreme reproductive behavior (Kuntner and Coddington, 2020). The causes and consequences of these relationships, however, remain obscure and require testing in a system with a strong hypothesis of evolutionary relationships coincident with species-level variation. We now have the former requirement (Yu et al., 2024), but unfortunately, the number of species for which we have behavioral and ecological data remains dismally low.

The often-high abundance and large size of Dolomedes make them inviting prey for birds and hosts for the growing larvae of pompilid wasps. The pattern of generalists and specialists in pompilid wasp parasitism observed in New Zealand and the USA likely varies in other regions, especially areas of high Dolomedes diversity such as Africa or Asia. Knowledge of prey for many pompilid species in Britain and Ireland are missing (O’Hanlon and O’Connor, 2021), and in New Zealand, there is call for more thorough documentation of pompilid prey (Thompson, 2020) as it may provide insight into species-level divergence in morphology, microhabitat use, and other behavior. Furthermore, the importance of predation pressure in microhabitat choice, phenology, activity cycles, and more remain to be explored. Such information will be especially informative when elucidating the conservation status of species and populations and when developing interventions that might mitigate their conservation risk.

These large spiders are not only prey, but are presumably important predators in their aquatic and terrestrial environments as well. Future directions related to their importance as predators could include molecular gut content analyses through metabarcoding to examine their role in ecosystems, including their potential role in controlling pest species.

Fishing spiders have fascinated scientists for decades with their ability to move on water and detect surface vibrations. The literature on Dolomedes sensory capabilities is extensive, yet incomplete and provides a great basis for follow-up studies on sensory physiology, especially studies that compare across species with different lifestyles and those that focus explicitly on vision as well as sensory processing. Future research could also explore the biomechanics of submerging and re-emerging from water, and biomimetic studies of artificial water-surface locomotion may inspire innovative robotic designs.

Many opportunities exist to further investigate parental care behavior in Dolomedes. Studies could explore the metabolic or biomechanical costs of taking an egg sac underwater and how the tradeoff between reduced foraging and increased offspring survival during nursery web guarding varies by female size and species. Spence et al. (1996), for example, found that food availability increasingly restricts fecundity in D. triton as size increases.

Given our collective expertise in behavioral ecology, we identify Dolomedes as an excellent taxon for studying reproductive behavior, particularly sexual cannibalism. Investigating more species could help test hypotheses about the evolution and function of both pre- and post-copulatory cannibalism (Burke, 2024). While the role of aggressive spillover in pre-copulatory cannibalism remains uncertain (Johnson and Sih, 2005; Kralj-Fišer et al., 2013, Kralj-Fišer et al., 2016), there is substantial evidence that post-copulatory sexual cannibalism is adaptive, even for males (Schwartz et al., 2016). It would be valuable to address how sexual selection relates to sexual cannibalism rates and whether any other Dolomedes species shows male complicity in cannibalism. Dolomedes have also been at the forefront of personality research, as female aggression in foraging is highly repeatable and sometimes correlated with sexual aggressiveness. Additional research topics could include the role of sexual selection on sperm competition, paternal investment, and mating systems. Most current studies on reproductive behavior of spiders focus on web-building families. Studying Dolomedes, a free-roaming predator, will broaden our understanding of mating behavior and its dependence on other behavioral ecology and life-history traits.