Once established, controlling a population of invasive species to minimize ecological and economic damage is difficult. Suppressing or eradicating the population(s) usually requires sustained, long-term investment. While Fantle-Lepczyk et al. (2022) estimate that only 4% of costs for invasive species go to control efforts, the absolute cost for agencies or land managers controlling invasive species can be burdensome (Larson et al., 2011). Despite the investment, suppression and/or eradication continue to be the primary goal of many invasive species management programs (Green and Grosholz, 2021). Thus, optimizing control efforts can be a high priority for invasive species managers. Optimization depends on control and removal methods (e.g., physical removal, chemical control, biological control) as well as a species’ life history traits. For example, in some cases, removing individuals of a certain life stage or age class from an invasive population can actually result in an increase in the population growth rate as a result of density-dependent release (Govindarajulu et al., 2005; Zipkin et al., 2009).

Optimizing captures often focuses on understanding the behavior of an invasive species (King et al., 2009; Bravener and McLaughlin, 2013), which involves testing various chemical or pheromone attractants (e.g., for invasive insects), or identifying physiological cues that will lure individuals into traps such as auditory, olfactory, vomerolfactory, or gustatory lures (Campbell et al., 2012; Lavelle et al., 2017). For example, in a study of invasive green crabs off the coast of Newfoundland, researchers found that using squid or cod increased green crab captures by 47% and 77% respectively, compared to the control bait of herring, which is typically used in removal efforts, and that these baits also led to captures of larger crabs (Favaro et al., 2020). For the invasive brown tree snakes on the island of Guam, extensive studies have been conducted to determine the optimal lure, and this research has led to using live or dead mice in the majority of control efforts (Clark et al., 2017). Ultimately, if removal of an invasive species is a primary goal for management, identifying attractants can increase the probability of reaching this goal.

Tegu lizards are an example of an invasive species that can be removed via trapping (Haro et al., 2020; Udell et al., 2022). Three species of tegus that are common in the pet trade have, or are at risk of, establishing invasive populations in the United States (U.S.) and other countries (Gaiotto et al., 2020). The Argentine black and white tegu (Salvator merianae) has established populations in four Florida counties (Engeman et al., 2011; Harvey et al., 2021) as well as one county in Georgia (Haro et al., 2020). Sightings continue to increase across the southern United States in particular, including new, ecologically sensitive areas of Florida (Sandfoss et al., 2025). The gold tegu (Tupinambus teguixin) has established a single population in southern Florida as well (Edwards et al., 2017), and while there are no established populations of the red tegu (Salvator rufescens) confirmed in the United States, there have been multiple sightings (EDDMapS, 2025). Recent projections suggest that much of the United States contains suitable habitat for all three species (Jarnevich et al., 2018), and that suitability will likely increase in the future (Kissel et al., 2025). Similar to other invasive reptiles (e.g., brown treesnakes [Savidge, 1987], Burmese pythons [Guzy et al., 2023]), tegu lizards have the potential to cause substantial ecological and economic damage (Klug et al., 2015), given they are a generalist omnivore (Figueroa et al., 2025; Gaiotto et al., 2020; Harman et al., 2025; Offner and Johnson, 2021) with broad physiological tolerances (Currylow et al., 2021; Goetz et al., 2021). They have been sighted on poultry farms as well (Haro et al., 2020), and identified as an economic threat due to their attraction to eggs.

Typically, a single chicken egg is used as a lure in trapping and removal efforts for tegus (Avery et al., 2016; Haro et al., 2020; Udell et al., 2022). Chicken eggs, along with squid, and chicken meat have been used as bait to trap other invasive carnivorous lizards in Florida as well (Cambell, 2005). However, it is unknown as to whether tegus are attracted via olfactory or visual senses, or both. Avery et al. (2016) tested melon-scented oil and mouse paste as alternative lures, but these were no more effective than chicken eggs. A recent y-maze experiment tested vomerolfactory, olfactory, and visual sensory cues in S. merianae, and a field study tested different scent lures (blueberry oil or mouse oil), but no clear patterns emerged (Xiong, 2025). Experiments to test olfactory cues of other invasive reptiles, such as the Burmese python, have found that pythons are not attracted to rabbit feces, urine or hair, suggesting that olfactory cues are not the primary lure for this species (Miller et al., 2025). In general, there have been few experiments to manipulate the visual or olfactory cue of lures to determine the mechanisms behind attractants for invasive reptiles.

Currently, there are extensive trapping efforts led by the National Park Service (NPS) and Florida Fish and Wildlife Conservation Commission (FWC) to prevent tegus from establishing in Everglades National Park (ENP). Trapping within ENP and along the park’s boundary commenced in 2019, has continued annually, and has largely kept the population from spreading deeper into ENP, despite a dense population just to the east of the park boundary (Sandfoss et al., 2025). Managers deploy traps with a single chicken egg as a lure, and while generally successful at capturing tegus, non-target species are also caught in the traps, which can reduce availability of the traps for tegus.

To test whether using different combinations of real and decoy eggs affected tegu or non-target species captures, we used two years of data in which traps were randomly deployed by NPS staff with either a single real chicken egg (control), three real chicken eggs (representing an increase in olfactory and visual cues), a single real chicken egg and either a single decoy egg or two decoy eggs (increase in visual cue with the standard olfactory cue), or three decoy eggs (representing only a visual cue). We did not have a treatment that increased olfactory cues without a corresponding increase in visual cue because this was not possible with the bait we used for our study (i.e., eggs). Our objectives were to understand whether different combinations of real and decoy eggs could increase tegu capture probability while minimizing non-target captures and provide a more cost-effective alternative to chicken eggs (i.e., reusable decoy eggs). This was of particular concern to managers given rising costs and reduced availability of chicken eggs in 2023, due in part to an outbreak of avian influenza.

Our Bayesian linear random-effects models accounted for multiple factors influencing capture probabilities and allowed for direct comparisons between tegu and non-target models using posterior distributions (Hobbs and Hooten, 2015). Despite variation in deployment duration across treatments, our sample sizes (e.g., number of traps deployed with each bait type) were sufficient for model convergence and provided informative estimates. Our results demonstrate that baiting traps with three real chicken eggs significantly increased the probability of capturing tegus (by ~33%), without a corresponding increase in non-target capture probability (Figure 2). In contrast, treatments combining one real egg with one or two decoy eggs increased non-target capture probability but did not improve tegu capture probability (Figure 2). The three decoy egg treatment resulted in lowest capture probabilities for both tegus and non-targets (Figure 2). Overall, these findings indicate that an increase in visual cues alone while keeping the olfactory cue constant (i.e., a single chicken egg with one or more decoy eggs) did not increase tegu capture probabilities, nor did a larger visual cue without an olfactory cue (three decoy eggs). An increase in olfactory stimuli (i.e., three real eggs) appears to be most effective, supporting the hypothesis that tegus rely primarily on olfactory cues when locating bait. An alternative hypothesis is that the painted decoy eggs may give off a scent that could mask the chicken egg scent (partially or wholly) or act as a detractant (i.e., tegus are repelled by the scent of painted decoy eggs). This would align with our results suggesting that treatments without decoy eggs were generally more effective at capturing tegus than treatments with decoy eggs. This may indicate odor plays a key-role in long distance attraction, though further research can help to isolate specific chemical or sensory drivers.

We leveraged an on-going control effort to assess the effect of bait type on the probability of capture. This resulted in a tradeoff between study design and achieving management goals (i.e., maximizing removal and reducing effects to non-target species). For example, some treatments were confounded with year because the treatment had to be removed or modified based on real-time adaptive management decisions (refer to methods, Table 1). This confounding of treatments prevented us from directly assessing the effect of year on tegu capture probability. However, there was no statistical difference in tegu CPUE between years for individual traps in the ‘one egg’ treatment (the treatment with the most data for both years), indicating that our assumption that there was no difference in capture probability across years was likely reasonable. Additional, multi-year experiments with a balanced study design could further validate this assumption.

We found no difference in the size of tegus captured during the early season (when larger tegus are available for capture) as a function of bait type (Figure 3A). During the primary tegu season, there was a weakly positive association of longer SVLs for males and juveniles captured with the ‘three real eggs’ treatment compared to the ‘one real egg, two decoy eggs’ treatment. However, although females were larger in general, the relationship with bait type was the opposite; larger females were caught in the ‘one real egg, two decoy eggs’ as opposed to the ‘three real egg’ treatment (Figure 3B). These patterns suggest that smaller tegus are seeking ‘high reward’ meals (‘three real eggs’ treatment), consistent with foraging theory (Troyer, 1984; Wikelski et al., 1993), though the weak signal could benefit from additional targeted studies or experiments.

Trap type also influenced capture probability. Tegus were much less likely to be captured in medium single-door (SM) traps, which had relatively high non-target captures rates (Supplementary Figure S1). The M2DM2 trap style (medium single-door trap with modifications) had the highest tegu capture probability, while minimizing the capture probability of non-targets (Supplementary Figure S1). Although the probability of capturing non-targets was relatively high in the M2DM2 trap, it was lower than the probability of capturing non-target species in the XS2D and XS2DM2 trap styles, which also had lower probabilities of capturing tegus. These results suggest that pairing the M2DM2 trap type with three real eggs may maximize tegu capture efficiency while minimizing interference from non-target species.

Capture probability varied across sites. The C-111SW and C-111SE canals, and some trap locations within the AERO canal (Figure 1) had higher tegu capture probabilities, as suggested by the random intercept estimates (Supplementary Figure S2). While the variation in the probability for non-target capture was lower (Supplementary Figure S3), the C-111SW and C-111SE canals tended to have higher probabilities of non-target species capture as well, and L-31WS and L-31WN canals tended to have higher relative probability of non-target captures and lower relative probability of tegu captures (Supplementary Figures S2, 3). These spatial patterns suggest that trap deployment strategies could be refined by removing traps in locations with generally low-tegu and high non-target capture probabilities or optimizing trap and bait combinations in high-activity locations to reduce non-target interference (e.g., C-111SW and C-111SE).

Among non-target species, the hispid cotton rat was by far the most frequently captured, accounting for > 50% of non-target captures (Supplementary Table S2). Hispid cotton rats are generally common in Florida and throughout their range and are an International Union for Conservation of Nature species of least concern (The IUCN Red List of Threatened Species, 2026) and were released from the traps unharmed. The majority of non-target species, particularly the top two most common, are opportunistic generalist feeders that are likely to be captured with the use of any food bait. However, reducing the number of hispid cotton rat captures would likely significantly increase the amount of time that traps are available for tegus (i.e., not occupied). Eight of the non-target species captured were also non-native or invasive to Florida which were humanely euthanized. These made up 10% of captures (n = 34), suggesting that tegu trapping may offer secondary benefits by removing other invasive fauna. Four non-target species of special concern in Florida were captured (Florida box turtle [Terrapene carolina bauri], King rail [Rallus elegans], Peninsula cooter [Pseudemys peninsularis] and Eastern diamondback rattlesnake [Crotalus adamanteus]) (Sunquist-Blunden and Montero-McAllister, 2022) comprising 7.04% of non-target captures (n = 24). Most were Florida box turtles (n = 21); all were safely released without visible harm.

In addition to actual physical captures, we classified traps rendered non-functional by non-target disturbance as a non-target “capture”. These accounted for 37% of the 557 total non-target capture events. The ‘one real egg, two decoy eggs’ treatment had the highest number of both non-target captures and non-target trap disturbances, with trap disturbance rates more than ten times higher than any other treatment (Table 1). We hypothesize that the combination of olfactory cue given by the real egg and visual cue of the two decoy eggs may have attracted species such as raccoons, which attempted to extract the wired wooden eggs, resulting in flipped or triggered traps (Matlack et al., 2006; Piórkowska et al., 2024).

These findings have direct implications for both ongoing tegu control efforts and future early detection rapid response strategies. In rapid response scenarios, deploying medium, single door traps with modifications to decrease escape by smaller individuals, and baiting with three real eggs may maximize tegu capture probability. For long-term management, further research into methods for excluding frequent non-target species, particularly hispid cotton rats, could improve trap availability and efficiency. Although previous studies have found capsaicin treated baits ineffective at deterring non-targets (McBrayer et al., 2023), alternative scents or chemicals or trap modifications may be more effective. Additionally, identifying species with learned behavior that frequently disturb traps (e.g., raccoons) and developing mitigating strategies could enhance tegu trapping success (Roden-Reynolds et al., 2018). However, non-target captures might also be the result of behaviors and physiological needs unrelated to bait type (Spence-Bailey et al., 2010).

Overall, our study indicates that wooden decoy eggs in traps do not increase tegu capture probability and likely increase the probability of non-target capture or interference. While decoy eggs were tested as a cost-saving alternative to real eggs, the tradeoff in reduced tegu captures and increase in non-target activity may outweigh any financial benefit. By leveraging ongoing control efforts, we were able to evaluate bait types and trap styles in a real-world context. Our inferences can inform tegu management in other regions where tegu sightings are becoming more frequent (e.g., Georgia, South Carolina; Kissel et al., 2025) and contribute to broader efforts to refine trapping strategies (McBrayer et al., 2023) and understand the sensory mechanisms (e.g., olfactory vs. visual) that drive attraction in tegus (Avery et al., 2016).