This experiment was conducted on the campus of the University of Yaounde 1, where two carcasses of rats (Rattus norvegicus Berkenhout, 1769, var. Wistar), each weighing approximately 350 g, were used as models in the research experiment. The carcasses were exposed inside one wooden cage (150 cm × 150 cm × 150 cm) into a bush opposite Amphitheater 502 of the Faculty of Science (11°33′01″ E–3°51′35″ N; altitude, 720 m), from March 18 to June 12, 2023. The climate of this area is described as “Yaoundean type,” which is characterized by four distinct seasons of unequal duration: a long dry season from mid-November to mid-March, a short rainy season from mid-March to mid-June, a short dry season from mid-June to mid-August, and a long rainy season from mid-August to the end of October. The average annual rainfall fluctuates between 1,600 and 2,000 mm, while the average annual temperature varies between 22°C and 42°C (Kengne and Atangana, 2010; Abessolo et al., 2015). The vegetation/landscape of this part of the campus is dominated mainly by the presence of Elaeis guineensis Jacq, 1763, Musa sp., Ipomea batatas Lam, 1793, and Zea mays Linné, 1753.

The 3-month-old rats (R. norvegicus Berkenhout, 1769, var. Wistar) were brought to the site, weighed, and euthanized by a veterinarian according to ethical rules of the management of animals. Immediately, the rat carcasses were placed inside the cage, the sampling protocols of which followed those of Carvalho et al. (2004). The ambient air temperature was registered every day with a thermo-hygrometer placed inside the cage. The sampling of flying insects was undertaken three times daily during the first postmortem week using a combined method of mosquito nets, hand picking with flexible forceps, and a pitfall trap once daily until the disappearance of all soft tissue (the skeletonized stage). Subsequently, the insect samples were stored in 70% ethanol for identification using a binocular stereomicroscope according to the identification key of Delvare and Alberlenc (1989); Kurahashi and Kirk-Spriggs (2006); Whitworth (2010); Irish et al. (2014), and Rochefort et al. (2015).

Observations of the physical modifications that occurred during the corpse decay yielded five distinct alteration stages: the fresh stage, which lasted for 2 days (days 1 and 2); the bloated stage, from day 3 to day 4; the putrefied stage, from day 5 to day 9; the dried stage, which lasted from day 10 to day 61; and the last stage, called the skeletonized stage, which started from day 62 to the end of the decomposition of the carcasses ( Table 1 ). This finding on the decay process segmentation is in parallel with the recognition made by Dekeirsschieter et al. (2012); Shaalan et al. (2017); de A Azevedo et al. (2018); Gelderman et al. (2021), and Zongo et al. (2023), although the names of the stages varied. However, Schieweck et al. (2024) and Taleb et al. (2017) identified three and four steps, respectively. This inconsistency may be understood as a result of the geographic variations of the abiotic parameters linked to each experimental site, as the process of corpse alteration is typically related to environmental factors.

Table 1 provides a summary of the specific insects according to the state of decay. The fresh state was dominated by the family Calliphoridae (Hemipyrellia fernandica and Chrysomya albiceps), while the bloated state was dominated by Calliphoridae (Chrysomya laxifrons), Muscidae (Musca sp., Ophyra sp., and Hydrotaea sp.), Formicidae (Paratrechina weissi, Cardiocondyla emeryi, Plagiolepis brunni, and Oecophylla longinoda), and the first appearance of Staphylinidae, Histeridae, and Trogidae. The putrefaction phase was dominated by the families Muscidae (Atherigona sp.), Sarcophagidae (Sarcophaga africa), Braconidae (Coelalysia nigriceps), Sepsidae (Sepsis sp.), and Formicidae (Monomorium exiguum and Lepisiota sp.). The dried stage was colonized by the families Sphaeroceridae, Tenebrionidae, Scarabaeidae, Anthomyiidae, Sarcophagidae (Sarcophaga zumpti and Sarcophaga inaequalis), and Cleridae (Necrobia rufipes), while the skeletonization phase was characterized by the families Ptiliidae, Enicocephalidae, Tipulidae, Dermestidae, Cleridae, and Lygaeidae. This relation of the necroentomofauna to the state of the decay process can be used to estimate the time of death, the cause of death, and the place of death. The high diversity of cadaver-related fauna is in line with the results obtained by Dao et al. (2018); Feugang Youmessi et al. (2021); Irish et al. (2014); Koffi et al. (2017), and Rochefort et al. (2015) in the Ivory Coast, in Cameroon, and in South Africa.

Similar to Geissenberger et al. (2024); de A Azevedo et al. (2018), and Ourrad et al. (2022), this fauna belongs to several trophic guilds such as necrophages, predators, omnivores, saprophages, opportunists, parasitoids, hematophages, and accidental hosts, among which necrophages are the most important insects used for forensic entomology during crime scene investigations on wildlife animals/domestic animals.

The predictable succession patterns of silent witnesses of the crime scene, called corpse feeders in the present research, are consistent with the patterns obtained around the world, even though the taxonomic aggregation/assemblage of the two main taxa (Diptera and Coleoptera) were different. This difference of the families in these orders can be explained by the divergence of the environmental characteristics, such as the climate (temperature, relative humidity, wind speed, and pluviometry, among others), the sampling artifacts, and the size of the biological model used, as emphasized by Geissenberger et al. (2024); Thümmela et al. (2024), and Naman et al. (2024).

We recorded a total of 2,345 insects, shared between 3 classes, 13 orders, 37 families, 14 genera, and 27 species ( Table 2 ). Other researchers captured more corpse feeders: de A Azevedo et al. (2018) gathered 10,559 individuals, while Taleb et al. (2017) sampled 8,817 individuals. This variation in number could be the consequence of several scales related to abiotic variables and to interspecific competition within the necroentomofauna assemblages/communities, as well as to specific disturbances as co-inhabiting species are in permanent competition. Each degradation level was endorsed by some specific cadaveric fauna, as reported by Feugang Youmessi (2014) and Schieweck et al. (2024). Hence, the first and second postmortem days can be dated with the presence of H. fernandica, C. albiceps, Chrysomya putoria, Lucilia cuprina, Lucilia sp., and Chrysomya sp. (Calliphoridae). Days 3 and 4 can be dated with the presence of Chrysomya laxifrons (Calliphoridae), Musca sp., Ophyra sp., Hydrotaea sp. (Muscidae), P. weissi, C. emeryi, P. brunni, O. longinoda (Formicidae), Staphylinidae, Histeridae, and Trogidae. From day 5 to day 9, species such as Atherigona sp. (Muscidae), S. africa (Sarcophagidae), C. nigriceps (Braconidae), Sepsis sp. (Sepsidae), M. exiguum, and Lepisiota sp. (Formicidae) can be found. Species such as S. zumpti, S. inaequalis (Sarcophagidae), N. rufipes (Cleridae), Sphaeroceridae, Tenebrionidae, Scarabaeidae, and Anthomyiidae comprised the fauna found from day 10 to postmortem day 61, while day 62 to the end of the decomposition are characterized by the presence of Ptiliidae, Enicocephalidae, Dermestidae, Cleridae, Tipulidae, and Lygaeidae. This postmortem estimation is in line with the results observed by Dao et al. (2018); Feugang Youmessi (2023, 2024), Koffi et al. (2017); Rochefort et al. (2015), and Zongo et al. (2023) in the Ivory Coast, in Cameroon, in South Africa, and in Burkina Faso.

Among the cadaveric organisms, Diptera (Calliphoridae) was the dominant family, followed by Coleoptera or beetles, corroborating the results of other experiments in Cameroon (Fantio et al., 2022; Feugang Youmessi et al., 2021; Feugang Youmessi, 2023; Feugang Youmessi and Djonga, 2024; Djonga, 2024), Africa (Koffi et al., 2017; Zongo et al., 2023; Naman et al., 2024; Taleb et al., 2017; Yapo et al., 2017), and worldwide (de A Azevedo et al., 2018; Amendt et al., 2004; Anderson, 2020; Lutz et al., 2017, 2019; Maisonhaute and Forbes, 2020; Ourrad et al., 2022).

Similar to Geissenberger et al. (2024); de A Azevedo et al. (2018), and Ouiza et al. (op. cit.), this fauna belongs to several trophic guilds such as necrophagous, predators, omnivorous, saprophagous, opportunists, parasitoids, hematophagous and accidentals, among which the necrophages are the most important insects in forensic entomology.