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Larvae of several blowfly species grow on carcasses and actively aggregate together. They face harsh developmental conditions resulting in a strong pressure to reduce development time: this is achieved either through thermoregulation or aggregation. We investigate how these two developmental strategies are modulated within heterospecific groups. In a first experiment, larvae of two species with different thermal requirements were deposited simultaneously on a thermal gradient. This resulted in the formation of two monospecific groups, each located at the species-specific thermal preferendum. However, when Calliphora vomitoria (Linnaeus) larvae were placed first, the later arriving Lucilia sericata (Meigen) larvae attracted the whole group to its own thermal preferendum. In the reverse experiment, half of the replicates resulted in single dense heterospecific groups observed at temperatures ranging from C. vomitoria to L. sericata preferendum. The other half of the replicates resulted in loose groups spread out on the thermal gradient. These results highlight the emergence of collective decisions ranging from thermal optimization to heterospecific aggregation at suboptimal temperatures. They demonstrate that species settlement order strongly affects self-organization processes and mixed-species group formation. We conclude that thermal optimization and heterospecific niche construction are two developmental strategies of carrion fly larvae. This article is part of the theme issue 'Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes'.

Chemical signals are widespread in insects, but those resulting in interspecific communication (i.e., synomones) remain understudied. Here, we analysed chemicals left on substrates by two species of blow fly larvae, Lucilia sericata (Meigen) and Calliphora vomitoria (Linneaus) (Diptera: Calliphoridae), which can aggregate together on carrion. Using solid-phase microextraction and dynamic headspace analysis, we identified six compounds common to both species: the decanoic, tetradecanoic, pentadecanoic, hexadecanoic and octadecanoic acids, and the 2-ethylhexyl salicylate. We then tested the behavioural effects of the decanoic and pentadecanoic acids using binary-choice experiments, along with the (Z)-9-tricosene, a pheromone found in many arthropods. The time spent by a larva and its average crawling speed were measured in two sides of an arena, where only one contained a compound at 0.25 or 25 μg/μl. No effect was observed when testing the decanoic acid. The pentadecanoic acid only reduced the speed of C. vomitoria larvae at 25 μg/μl. Finally, L. sericata larvae spent less time in the side containing the (Z)-9-tricosene at 0.25 μg/μl, whereas C. vomitoria spent more time and crawled faster in this side at 25 μg/μl. Although these results did not directly evidence synomones, they suggest that the (Z)-9-tricosene could regulate larval aggregations on carrion., (© 2022 Royal Entomological Society.)

Childhood is an ontogenetic stage unique to the modern human life history pattern. It enables the still dependent infants to achieve an extended rapid brain growth, slow somatic maturation, while benefitting from provisioning, transitional feeding, and protection from other group members. This tipping point in the evolution of human ontogeny likely emerged from early Homo. The GAR IVE hemi-mandible (1.8 Ma, Melka Kunture, Ethiopia) represents one of the rarely preserved early Homo infants (~ 3 years at death), recovered in a richly documented Oldowan archaeological context. Yet, based on the sole external inspection of its teeth, GAR IVE was diagnosed with a rare genetic disease-amelogenesis imperfecta (AI)-altering enamel. Since it may have impacted the child's survival, this diagnosis deserves deeper examination. Here, we reassess and refute this diagnosis and all associated interpretations, using an unprecedented multidisciplinary approach combining an in-depth analysis of GAR IVE (synchrotron imaging) and associated fauna. Some of the traits previously considered as diagnostic of AI can be better explained by normal growth or taphonomy, which calls for caution when diagnosing pathologies on fossils. We compare GAR IVE's dental development to other fossil hominins, and discuss the implications for the emergence of childhood in early Homo., (© 2021. The Author(s).)

Several studies have highlighted the impact of environmental factors such as food type or larval density on the development of blowfly larvae. We investigated how changes in development speed (due to larval density and group composition) are divided among feeding and post-feeding stages. Even if these parameters impinge only on feeding larvae, they may ultimately also affect their subsequent development, and especially metamorphosis duration. Therefore, this study analysed the effect of larval density and group composition on the rhythm of necrophagous blowfly development. Based on laboratory studies, we highlighted that Calliphora vicina individuals with a fast development during their feeding phase developed slower in the later post-feeding phase (i.e., they had a compensatory effect). Lucilia sericata, a calliphorid species also frequently found on carrion at the same time as C. vicina, showed a different developmental strategy by not making its post-larval development speed dependent on the larval development speed. Finally, while a compensatory effect may exist, variations in the development rate more often accumulate through life-stages and resulted in a larger variability for later development instars. In this respect, the inclusion of detailed development duration covering all life stages, including post-feeding, is recommended in future studies, especially those dedicated to forensic entomology., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Collective decisions have been extensively studied in arthropods, but they remain poorly understood in heterospecific groups. This study was designed to (1) assess the collective behaviours of blow fly larvae (Diptera: Calliphoridae) in groups varying in density and species composition, and (2) relate them to the costs and benefits of aggregating on fresh or decomposed food. First, experiments testing conspecific groups of Lucilia sericata and Calliphora vicina larvae, two species feeding at the same time on fresh carcasses, demonstrated decreases in growth and survival on rotten beef liver compared with fresh liver. However, mixing species together reduced this adverse impact of decomposition by increasing the mass of emerged adults. Second, larval groups were observed in binary choice tests between fresh and rotten liver (i.e. optimal and sub-optimal food sources). The results showed that larvae interacted with each other and that these interactions influenced their food preferences. We observed that (1) larvae were able to collectively choose the optimal food, (2) their choice accuracy increased with larval density and (3) the presence of another species induced a reversal in larval preference towards rotten food. These results highlight the ubiquity of collective decision properties in gregarious insects. They also reveal an unexpected effect of interspecific association, suggesting the colonization of new resources through a developmental niche construction., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2021. Published by The Company of Biologists Ltd.)

Necrophagous blowflies (Diptera: Calliphoridae) such as Calliphora vicina, a cold-tolerant species, and Lucilia sericata, a warm-adapted species, are pioneer carrion-breeder. Although these two species have different temperature preferences, larvae aggregate actively and often feed simultaneously on carrion. The hypothesis to be tested was that L. sericata benefits from the association with C. vicina at lower temperatures (i.e., 15 °C) and that C. vicina derives greater benefits from this association at higher temperatures (i.e., 28 °C). Therefore, both species were raised at these two constant temperatures from first instars to adults under three different conditions: monospecific low-density, monospecific high-density, and heterospecific high-density. The time until larval migration, surface area of puparia, and survival rates were determined for each condition. Differences between these fitness-related traits were found between species, temperatures, group densities, and species compositions. At 28 °C, C. vicina larvae bred in heterospecific groups migrated significantly earlier and in higher numbers than that under same density conspecific conditions, with a lower mortality rate. At 15 °C, both species benefited from high-density heterospecific associations, expressed by faster development and larger puparia. In conclusion, necrophagous larvae benefited from heterospecific aggregations at suboptimal temperatures by adapting their migration time to that of the faster species. Since temperature changes throughout the day and over the year, the beneficiary of such a collective association also changes. The costs involved and deviations to the temperature-size rule highlight the complexity of the carrion ecosystem., (© 2020 Institute of Zoology, Chinese Academy of Sciences.)

Measuring temperature is a key factor in forensic entomology. While noting factors to consider for a posteriori temperature estimation, many studies lack detailed methods or general rules allowing their integration into insect development-time calculations. This article proposes tools for determining the adequacy of weather station temperature datasets versus the local temperature experienced by carrion breeders. The idea is to start from a local scale (i.e., the cadaver) and gradually move to larger scales: at each step, the temperature can be increased, decreased or smoothed by environmental or biological factors. While a one-size-fits-all solution is not feasible for a complex and sensitive issue such as forensic meteorology, this checklist increases the reliability of minimum post-mortem interval (PMImin) estimation and the traceability of the proposed assumption.

Necrophagous insects are mostly known through forensic entomology. Indeed, experimental data investigating the effect of temperature on larval development underlies post-mortem interval estimations. However, such developmental studies rarely considered the behavior of maggots. In contrast, previous results supposed that calliphoridae larvae use behavioral strategies to optimize their development on carcasses. To test this idea, we analyzed the trade-off between thermal regulation (individual thermal preferences) and social behavior (aggregation) in Lucilia sericata larvae. The first set of experiments analyzed the behavior of third instars in response to thermal changes in their environment. The results demonstrated a clear thermoregulation behavior, supporting the assumption that larvae continuously move to reach a suitable internal temperature. The second set of experiments focused on the trade-off between thermal optimization and aggregation. The results showed a constant search for congeners and an attractiveness of aggregates, sometimes to the detriment of thermal optimization. Together, these results demonstrate a balance between behavioral thermoregulation and social strategies, two significant mechanisms for developmental optimization in necrophagous larvae. In conclusion, these findings highlights unexpected (social) strategies to cope with ephemeral resource and high selection pressure. They also raise important questions for forensic entomology.

The thermoregulation behavior of Lucilia sericata larvae (Diptera: Calliphoridae), a necrophagous species that feeds on vertebrate cadavers, was investigated. These larvae require high heat incomes to develop, and can elevate temperatures by forming large aggregates. We hypothesized that L. sericata larvae should continue to feed at temperatures up to 38 °C, which can be reached inside larval masses. Thermal regulation behavior such as movement between a hot food spot and colder areas was also postulated. The hypotheses were tested by tracking for 1 h the activity of single, starved third instar larvae in a Petri dish containing 1 food spot (FS) that was heated to a constant temperature of 25 °C, 34 °C or 38 °C with an ambient temperature of 25 °C. The influence of previous conspecific activity in the food on larval behavior was also tested. The crops of larvae were dissected to monitor food content in the digestive systems. Based on relative crop measurements, larvae fed at all food temperatures, but temperature strongly affected larval behavior and kinematics. The total time spent by larvae in FS and the duration of each stay decreased at high FS temperature. Previous activity of conspecifics in the food slightly increased the time spent by larvae in FS and also decreased the average distance to FS. Therefore, necrophagous L. sericata larvae likely thermoregulate during normal feeding activities by adjusting to local fluctuations in temperature, particularly inside maggot masses. By maintaining a steady internal body temperature, larvae likely reduce their development time., (© 2017 Institute of Zoology, Chinese Academy of Sciences.)

Necrophagous Calliphoridae breed in vertebrate carrion. Their larvae aggregate and form large masses of individuals. These aggregated larvae can reach adulthood faster than scattered larvae, increasing their chances of survival. Furthermore, the gathering of larvae of different species suggests possible interspecific aggregation vectors. In this context, the effect of larval ground-left cues on larvae of Calliphora vomitoria and Lucilia sericata was studied. We used video tracking to follow larvae placed in binary choice tests. We observed (1) a preference of both species for a side marked by conspecific or heterospecific larvae compared to an unmarked side, (2) a preference of L. sericata larvae for a conspecific-marked side compared to a heterospecific-marked side but only at high concentration of cues and (3) a preference of both species for the side marked by the greater number of larvae. These results demonstrate that larvae leave a mark locally which is retentive, has an interspecific range, has an effect proportional to its intensity and whose strength varies depending on the emitting species. According to the self-organization theory, this mark could enhance larval gathering and promote interspecific aggregations. While not yet demonstrated, an interspecific Allee effect could explain the interspecific association of necrophagous calliphorid larvae.

The use of insects as indicators of post-mortem displacement is discussed in many texts, courses and TV shows, and several studies addressing this issue have been published. Although the concept is widely cited, it is poorly understood, and only a few forensic cases have successfully applied such a method. The use of necrophagous insects as evidence of cadaver relocation actually involves a wide range of biological aspects. Distribution, microhabitat, phenology, behavioral ecology, and molecular analysis are among the research areas associated with this topic. This article provides the first review of the current knowledge and addresses the potential and limitations of different methods to evaluate their applicability. This work reveals numerous weaknesses and erroneous beliefs as well as many possibilities and research opportunities., Competing Interests: The authors declare that they have no competing interests.

Necrodes littoralis (Linnaeus, 1758) (Coleoptera: Silphidae), also known as the "shore sexton beetle," is a common silphid beetle that visits and breeds on large vertebrate cadavers. This study describes, for the first time, the involvement of N. littoralis on human corpses based on a large dataset of 154 French forensic cases. Various parameters regarding corpse location, decomposition stages, and entomofauna were extracted from each file. Compared to all of the forensic entomology cases analyzed between 1990 and 2013 (1028), N. littoralis was observed, on average, in one case out of eight; most of these cases occurred during spring and summer (73.5%). More than 90% of the cases were located outdoors, especially in woodlands, bushes, and fields. The decomposition stage of the corpse varied among cases, with more than 50% in the advanced decomposition stage, 36% in the early decomposition stage, and less than 10% in the fresh, mummified, or skeletonized stages. Regarding other necrophagous species sampled with N. littoralis, Calliphorid flies were found in 94% of the cases and Fanniidae/Muscidae in 65% of the cases. Chrysomya albiceps, a heliophilic species mostly located in the Mediterranean area, was present in 34% of the cases (only 20% in the whole dataset). The most common coleopteran species were Necrobia spp. (Coleoptera: Cleridae) and Creophilus maxillosus (Coleoptera: Staphylinidae); these beetles were observed in 27% of the cases. The over-representation of these species is likely due to similar requirements regarding the climate and decomposition stage. As N. littoralis is frequently observed and tends to become more common, we conclude that the developmental data for this species would be a precious tool for forensic entomologists in Europe.

This study was designed to examine the common belief that necrophagous blowflies lay their eggs in wounds. The egg-laying behaviour of Lucilia sericata was observed under controlled conditions on wet, artificially wounded or short-haired areas of rat cadavers. Flies laid significantly more eggs on the wet area and the area with short hair than on the dry area or area with long hair. No eggs were observed inside the wounds in any of the replicates. The effect of egg immersion (body fluids often exudes in wounds) on the survival rate of larvae was also investigated. In low water condition, an average of 72.7±7.9% of the larvae survived and they reached a mean length of 7.5±0.6mm. In contrast, submerging eggs under a high volume of water strongly affected their survival rate (25±3.7%) and development. Similar results were observed using unfrozen pig blood instead of water. These data question the information found in the literature regarding the preferential egg-laying behaviour of Calliphorids flies in wounds., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Several parameters can delay the first arrival of flies on a corpse and the subsequent development of the larvae. This study focuses on the development of Lucilia sericata (Diptera: Calliphoridae) (Meigen, 1826) on household chemical-contaminated substrates. bleach, perfume, hydrochloric acid, caustic soda, insecticide, mosquito repellent, and gasoline in quantities consistent with an amount that could possibly be spilled on a corpse were mixed with beef liver to simulate contaminated fleshes. Larvae were bred at 25 °C on these media until emergence. Four developmental parameters were followed: survival rates, development times, sex ratios, and adult sizes. Hydrochloric acid, insecticide, and gasoline killed all larvae. In low quantities, caustic soda and mosquito repellent increased the development time and decreased the adult size. However, high quantities of these chemicals killed all larvae. Lastly, bleach and perfume did not affect the survival rate and barely impacted the development time or adult size. These results demonstrate common household products spilled on a corpse can strongly affect the development of Calliphoridae larvae. The effects of such products should be considered in forensic entomology cases., (© 2014 American Academy of Forensic Sciences.)

From 1994 to 2013, French forensic entomology laboratories investigated 1,093 cases. Larder beetles (Coleoptera: Dermestidae) were observed in 81 (7.5%) of these cases. To describe and analyze these 81 cases, eight parameters were used: city, location (indoor or outdoor), decay stage (fresh, decay, or dry), dermestid species and instar (adults and/or larvae), presence of living calliphorid larvae, presence of calliphorid pupae or adults, and presence of other necrophagous species. Eight Dermestidae species were observed: Dermestes frischii (42% of cases), Dermestes undulatus (35.8%), Dermestes peruvianus (12.3%), Dermestes lardarius (9.9%), Dermestes haemorrhoidalis (8.6%), Dermestes maculatus (7.4%), Dermestes bicolor (3.7%), and Dermestes ater (1.2%). Larder beetles primarily developed on human cadavers in outdoor locations in areas with a dry climate and were never reported in oceanic areas (which are characterized by frequent rainfall and high ambient humidity). The number of dermestid species on a single corpse never exceeded three. Typically, one species was found per corpse. Species differed between indoor and outdoor cases, with D. frischii and D. undulatus dominant in outdoor cases, while D. peruvianus dominant in indoor cases. Calliphoridae was found in 88% of the cases, while Hydrotaea and Piophilidae were observed 40% of the time. Regarding Coleoptera, Necrobia spp. (Coleoptera: Cleridae) was observed in 46% of the cases. Lastly, we observed a typical decomposition pattern, with preferential feeding areas on the face, hands, and feet (i.e., the extremities). Pupation chambers on or inside the bones were not observed.

Human remains found in aquatic contexts are frequently recovered incomplete and badly decomposed, and therefore present a challenge for medico-legal institutes as their possibilities of analysis for identification and investigation of cause and manner of death are limited. This article aims to demonstrate the potential of forensic examination and analyses (DNA, toxicology, diatoms and entomology) on a set of bones recovered from a river in Strasbourg and the possibility to trigger identification of the victim and circumstances of death despite the state of decomposition and incompleteness of remains., (Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.)

Larvae of the necrophagous Blowfly Lucilia sericata (Diptera Calliphoridae) live on vertebrate cadavers. Although continuously feeding was previously assumed for this species, we hypothesized that larvae do not feed constantly. According to this hypothesis, their crop should not always be full, which should be reflected in crop surfaces. We dissected and measured the crops of larvae of the same age and bred in the same conditions. Crop surfaces of 117 larvae just removed from the food ranged from 0 to 16.6 mm(2) (mean=5.325±2.84 mm(2)). The distribution of these crop surfaces indicates a continuous variation of satiation/feeding activity in the population. Starving experiments showed a quite long digestive process. After 90 min of starving, the decrease in crop surfaces became obvious, but 150 min were necessary to observe more than a half of the population with an empty crop (less than 2 mm(2)). No more differences were observed after 150, 180 and 240 min of starving. We finally used starved larvae to observe the kinetic of food absorption and the duration of the food-intake phase. Our results indicates that larvae can ingest faster than they digest. After 5 min spent in the food, 70% of the larvae had a crop surface larger or equal to 8 mm(2). We observed for the first time an over-feeding of the larvae, with high crop surfaces overrepresented compared to larvae never starved (control). Together, these results indicate that larvae do not feed continuously, and regulate their foraging behavior. We propose that the foraging behavior of the larvae creates a permanent movement inside the larval masses. This turnover/scramble competition may be linked to the larval-mass effect, i.e. the local temperature increase observed in large necrophagous larvae aggregates., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Numerous Calliphoridae species larvae are necrophageous and develop on animal cadavers. During the feeding stages, a strong gregarious behaviour leads to the formation of large larval masses, allowing larvae to share digestive fluids. Furthermore, a mass of larvae emits heat, resulting in a local increase of temperature. Differences greater than 20°C between ambient and larval mass temperatures have already been observed, and the temperature of the mass can reach 50°C. Thus, larvae could benefit from this increased local temperature to speed up their development. This study focuses on the dynamic and characterisation of heat emission by Lucilia sericata (Diptera: Calliphoridae) (Meigen, 1826) larval masses. Experiments were performed under controlled conditions using several ambient temperatures and different numbers of larvae. Results indicate that heat emission depends on the instar and is strongly affected by available amount of food. Furthermore, according to the experimental data, the heat emission is also relative to the weight of the larval mass, the larvae number and the local temperature. These results also demonstrate that optimum ambient-temperature values ranging between 22°C and 25°C produce maximal heat-emission per larva. Furthermore, a feedback loop, involving heat exchanges and physiological and behavioural thermoregulation processes, appears inside aggregates. In the context of forensic cases and post-mortem interval (PMI) estimation, these results indicate that heat emission can occur even with "small" masses if they are composed of high number of second stage larvae. Furthermore, particular attention should be paid on cases involving L. sericata larvae at ambient temperature ranging from 22°C to 25°C, which appears to maximise the heat-emission process., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

The most common task of a forensic entomologist is to determine an accurate minimum post-mortem interval (PMI) using necrophagous fly larvae found on carrion. More often, blowflies (Diptera: Calliphoridae) are the first insects to detect the cadaver and, if the circumstances are favourable, to leave eggs on the body. However, several studies reveal that products such as gas or paint found on the cadaver induce a delay in the colonisation of the body, leading to an under-estimate of the PMI. Six common household products (gas, mosquito citronella repellent, perfume, bleach, hydrochloric acid and soda) were added to dead rats (Rattus norvegicus) in a field (Lille Forensic Institute, France). The presence of necrophagous flies was checked at regular intervals during 1 month. This experiment was repeated at the same period for four consecutive years. Results clearly showed the repellent effect of three of the six tested substances: gas (petroleum spirit), perfume and mosquito citronella repellent, which resulted in a mean delay of several days in the appearance of the first Dipteran species. Experiments were then carried out in controlled conditions in order to confirm previous observations. An olfactometer was specially designed to observe the behaviour of female Calliphora vicina (Diptera: Calliphoridae) in response to mice (Mus musculus) cadaver odour stimuli combined with household products. Dead mouse odour was a strong attractive stimulus for most of the tested individuals. Furthermore, it was noticed that the presence of mosquito citronella repellent, perfume, hydrochloric acid and paradichlorobenzene produced a significant repellent effect on female flies. All these results together confirm the repellent effect of some household products on flies and the necessity for forensic entomologists to consider this hypothesis when estimating the PMI.

This work investigates variation in the crawling speed of Protophormia terraenovae larvae (Robineau-Desvoidy) (Diptera Calliphoridae) as a function of body length and ambient temperature. A video-tracking system was used to follow the movement of larvae in an experimental arena, and to estimate their average crawling speed. Recordings were carried out at various temperatures using larvae of different developmental stages. As temperature increased, the larvae crawled at a faster speed. Furthermore, speed increased as a function of body length. We present a general allometric relationship to express the average crawling speed of larvae as a combined function of temperature and body length, expressed in the following equation: speed (cm/min)=5.45 x log[length (mm)]+0.66 x temperature (degrees C)-12.8. These results are particularly useful in forensic entomology for estimating the time that elapsed following the larva's departure from the corpse. This information can provide more accuracy for post-mortem interval estimations and a better comprehension of larvae behaviour and displacement.