Managing the risks and rewards of death in eusocial insects

The Impact of Termiticides on Termite Corpse Management

Soil treatments and baits are two primary chemical control strategies for subterranean termites. Baiting is targeted and eco-friendly but requires ongoing maintenance, while soil treatments provide immediate, long-lasting protection with potential environmental concerns. Previously, we found that termites differentially manage deceased individuals based on their postmortem chemical signatures, potentially circumventing chemical controls. Given the distinct differences in the synthetic termiticides used for soil treatments (fast-acting) and baits (slow-releasing), we hypothesized that termites would respond differently to corpses treated with these two methods. To test this hypothesis, in Reticulitermes flavipes, we (1) profiled postmortem chemicals in termites exposed to different termiticides and (2) documented live termite responses to these corpses. Significant variations in postmortem chemical signatures, particularly 3-octanol and 3-octanone, were found among termites exposed to different termiticides, especially bifenthrin and fipronil. However, these variations did not lead to significantly different undertaking behaviors, indicating a complex relationship between death cues and termite behavior. Contrary to our hypothesis, except for bifenthrin, the fundamental undertaking behaviors were consistent despite differences in retrieval timing. This suggests that termiticides alone do not fully dictate termite undertaking behavior. Understanding termite corpse management is crucial for evaluating termiticide effectiveness, highlighting the need for an integrated pest management approach.

Desert Ant (Melophorus bagoti) Dumpers Learn from Experience to Improve Waste Disposal and Show Spatial Fidelity

The Central Australian red honey-pot ant Melophorus bagoti maintains non-cryptic ground-nesting colonies in the semi-desert habitat, performing all the activities outside the nest during the hottest periods of summer days. These ants rely on path integration and view-based cues for navigation. They manage waste by taking out unwanted food, dead nestmates, and some other wastes, typically depositing such items at distances > 5 m from the nest entrance, a process called dumping. We found that over multiple runs, dumpers headed in the same general direction, showing sector fidelity. Experienced ants dumped waste more efficiently than naive ants. Naive individuals, lacking prior exposure to the outdoor environment around the nest, exhibited much scanning and meandering during waste disposal. In contrast, experienced ants dumped waste with straighter paths and a notable absence of scanning behaviour. Furthermore, experienced dumpers deposited waste at a greater distance from the nest compared to their naive counterparts. We also investigated the navigational knowledge of naive and experienced dumpers by displacing them 2 m away from the nest. Naive dumpers were not oriented towards the nest in their initial trajectory at any of the 2 m test locations, whereas experienced dumpers were oriented towards the nest at all test locations. Naive dumpers were nest-oriented as a group, however, at the test location nearest to where they dumped their waste. These differences suggest that in red honey ants, learning supports waste disposal, with dumping being refined through experience. Dumpers gain greater spatial knowledge through repeated runs outside the nest, contributing to successful homing behaviour.

Corpse-associated odours elicit avoidance in invasive ants

BACKGROUND

Invasive ants, such as Linepithema humile (the Argentine ant), pose a global threat, necessitating a better understanding of their behaviour in order to improve management strategies. Traditional eradication methods, including baiting, have had limited success, but the causes of control failure are not always clear. This study aims to investigate whether ants form associations between food odours and corpses, and subsequently avoid areas or food sources with food odours associated with corpses. We propose that ants may learn to avoid toxic baits in part because of their association with ant corpses, which could have implications for pest control strategies.

RESULTS

Ants were tested on a Y-maze after exposure to scented corpses or dummies. 69% (n = 64) of ants avoided branches bearing the scent of scented corpses. Colonies neglected food with corpse-associated odours, with only 42% (n = 273) of foragers feeding from such sources. However, if corpses were produced by feeding ants scented toxicant, focal ants encountering these corpses did not avoid the corpse-associated scent on a Y-maze (53%, n = 65). In dual-feeder tests, ants did not avoid feeding at food sources scented with odours associated with conspecific corpses.

CONCLUSION

Conspecific corpses act as a negative stimulus for ants in a foraging situation, potentially causing avoidance of toxic baits. This study suggests adding odours to baits and cycling them to disrupt the bait-corpse association may be helpful. Interestingly, although avoidance of baits was observed, feeding preferences were not significantly affected. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The influence of first desaturase subfamily genes on fatty acid synthesis, desiccation tolerance and inter-caste nutrient transfer in the termite Coptotermes formosanus

Desaturase enzymes play an essential role in the biosynthesis of unsaturated fatty acids (UFAs). In this study, we identified seven "first desaturase" subfamily genes (Cfor-desatA1, Cfor-desatA2-a, Cfor-desatA2-b, Cfor-desatB-a, Cfor-desatB-b, Cfor-desatD and Cfor-desatE) from the Formosan subterranean termite Coptotermes formosanus. These desaturases were highly expressed in the cuticle and fat body of C. formosanus. Inhibition of either the Cfor-desatA2-a or Cfor-desatA2-b gene resulted in a significant decrease in the contents of fatty acids (C16:0, C18:0, C18:1 and C18:2) in worker castes. Moreover, we observed that inhibition of most of desaturase genes identified in this study had a negative impact on the survival rate and desiccation tolerance of workers. Interestingly, when normal soldiers were reared together with dsCfor-desatA2-b-treated workers, they exhibited higher mortality, suggesting that desaturase had an impact on trophallaxis among C. formosanus castes. Our findings shed light on the novel roles of desaturase family genes in the eusocial termite C. formosanus.

Toxicity and Behavior-Altering Effects of Three Nanomaterials on Red Imported Fire Ants and Their Effectiveness in Combination with Indoxacarb

The red imported fire ant (Solenopsis invicta Buren) is one of the 100 worst invasive alien species in the world. At present, the control of red imported fire ants is still mainly based on chemical control, and the most commonly used is indoxacarb bait. In this study, the contact and feeding toxicity of 16 kinds of nanomaterials to workers, larvae, and reproductive ants were evaluated after 24 h, 48 h, and 72 h. The results showed that the mortality of diatomite, Silica (raspberry-shaped), and multi-walled carbon nanotubes among workers reached 98.67%, 97.33%, and 68%, respectively, after contact treatment of 72 h. The mortality of both larval and reproductive ants was less than 20% after 72 h of treatment. All mortality rates in the fed treatment group were below 20% after 72 h. Subsequently, we evaluated the digging, corpse-removal, and foraging behaviors of workers after feeding with diatomite, Silica (raspberry-shaped), and multi-walled carbon nanotubes for 24 h, which yielded inhibitory effects on the behavior of red imported fire ants. The most effective was diatomite, which dramatically decreased the number of workers that dug, extended the time needed for worker ant corpse removal and foraging activities, decreased the number of workers that foraged, and decreased the weight of the food carried by the workers. In addition, we also evaluated the contact and feeding toxicity of these three nanomaterials in combination with indoxacarb on red imported fire ants. According to contact toxicity, after 12 h of contact treatment, the death rate among the red imported fire ants exposed to the three materials combined with indoxacarb reached more than 97%. After 72 h of exposure treatment, the mortality rate of larvae was more than 73% when the nanomaterial content was above 1% and 83% when the diatomite content was 0.5%, which was significantly higher than the 50% recorded in the indoxacarb control group. After 72 h of feeding treatment, the mortality of diatomite, Silica (raspberry-shaped), and multi-walled carbon nanotubes combined with indoxacarb reached 92%, 87%, and 98%, respectively. The death rates of the three kinds of composite ants reached 97%, 67%, and 87%, respectively. The three kinds of composite food had significant inhibitory effects on the behavior of workers, and the trend was largely consistent with the effect of nanomaterials alone. This study provides technical support for the application of nanomaterials in red imported fire ant control.

Necrophagy by insects in Oculudentavis and other lizard body fossils preserved in Cretaceous amber

When a vertebrate carcass begins its decay in terrestrial environments, a succession of different necrophagous arthropod species, mainly insects, are attracted. Trophic aspects of the Mesozoic environments are of great comparative interest, to understand similarities and differences with extant counterparts. Here, we comprehensively study several exceptional Cretaceous amber pieces, in order to determine the early necrophagy by insects (flies in our case) on lizard specimens, ca. 99 Ma old. To obtain well-supported palaeoecological data from our amber assemblages, special attention has been paid in the analysis of the taphonomy, succession (stratigraphy), and content of the different amber layers, originally resin flows. In this respect, we revisited the concept of syninclusion, establishing two categories to make the palaeoecological inferences more accurate: eusyninclusions and parasyninclusions. We observe that resin acted as a "necrophagous trap". The lack of dipteran larvae and the presence of phorid flies indicates decay was in an early stage when the process was recorded. Similar patterns to those in our Cretaceous cases have been observed in Miocene ambers and actualistic experiments using sticky traps, which also act as "necrophagous traps"; for example, we observed that flies were indicative of the early necrophagous stage, but also ants. In contrast, the absence of ants in our Late Cretaceous cases confirms the rareness of ants during the Cretaceous and suggests that early ants lacked this trophic strategy, possibly related to their sociability and recruitment foraging strategies, which developed later in the dimensions we know them today. This situation potentially made necrophagy by insects less efficient in the Mesozoic.

Both age and social environment shape the phenotype of ant workers

Position within the social group has consequences on individual lifespans in diverse taxa. This is especially obvious in eusocial insects, where workers differ in both the tasks they perform and their aging rates. However, in eusocial wasps, bees and ants, the performed task usually depends strongly on age. As such, untangling the effects of social role and age on worker physiology is a key step towards understanding the coevolution of sociality and aging. We performed an experimental protocol that allowed a separate analysis of these two factors using four groups of black garden ant (Lasius niger) workers: young foragers, old foragers, young nest workers, and old nest workers. We highlighted age-related differences in the proteome and metabolome of workers that were primarily related to worker subcaste and only secondarily to age. The relative abundance of proteins and metabolites suggests an improved xenobiotic detoxification, and a fuel metabolism based more on lipid use than carbohydrate use in young ants, regardless of their social role. Regardless of age, proteins related to the digestive function were more abundant in nest workers than in foragers. Old foragers were mostly characterized by weak abundances of molecules with an antibiotic activity or involved in chemical communication. Finally, our results suggest that even in tiny insects, extended lifespan may require to mitigate cancer risks. This is consistent with results found in eusocial rodents and thus opens up the discussion of shared mechanisms among distant taxa and the influence of sociality on life history traits such as longevity.

Chemical cues in disease recognition and their immunomodulatory role in insects

Preventing infections is crucial for host fitness and many insects modify their behaviour upon sensing a contagion. We review chemical cues that mediate insect behaviour in response to parasites, and diseased or dead conspecifics. Considering the large diversity of behavioural disease defences described, surprisingly little is known about disease-associated cues that mediate them, especially their chemoreceptor and neuronal details. Interestingly, disease cues do not only modify host behaviour, but they could also play a direct role in immune system activation via neuroendocrine regulation, bypassing the need for risky immunological contact with the parasite. Such crosstalk is an exciting emerging research area in insect ecological immunology that should prove invaluable in studying host-parasite interactions by combining analytical methods from chemical ecology.

The Nasonov gland pheromone as a potential source of death cue in Apis cerana

The ability to detect and remove dead adult bees is an essential part of honeybee colony fitness that prevents the spread of pathogens. Fatty acid olfactory cues stimulate undertaking behavior among different social species within Hymenoptera, but the chemicals responsible for the death cue in Apis cerana have not yet been identified. We explored the Nasonov gland as a potential source of these chemicals in A. cerana. Gas chromatography indicated that unlike A. mellifera, the A. cerana Nasonov gland does not contain any volatile terpenes, only fatty acids. As a bioassay, dead honeybees were rinsed free of their individual cuticular hydrocarbons via dichloromethane and two concentrations of oleic acid and a synthetic blend of the Nasonov pheromone in A. cerana were applied to the dummies. Results showed that oleic acid did not stimulate corpse removal in A. cerana. However, the synthetic pheromone blend of A. cerana Nasonov did stimulate removal.

Death is common, so is understanding it: the concept of death in other species

Comparative thanatologists study the responses to the dead and the dying in nonhuman animals. Despite the wide variety of thanatological behaviours that have been documented in several different species, comparative thanatologists assume that the concept of death (CoD) is very difficult to acquire and will be a rare cognitive feat once we move past the human species. In this paper, we argue that this assumption is based on two forms of anthropocentrism: (1) an intellectual anthropocentrism, which leads to an over-intellectualisation of the CoD, and (2) an emotional anthropocentrism, which yields an excessive focus on grief as a reaction to death. Contrary to what these two forms of anthropocentrism suggest, we argue that the CoD requires relatively little cognitive complexity and that it can emerge independently from mourning behaviour. Moreover, if we turn towards the natural world, we can see that the minimal cognitive requirements for a CoD are in fact met by many nonhuman species and there are multiple learning pathways and opportunities for animals in the wild to develop a CoD. This allows us to conclude that the CoD will be relatively easy to acquire and, so, we can expect it to be fairly common in nature.

Dead cells release a 'necrosignal' that activates antibiotic survival pathways in bacterial swarms

Swarming is a form of collective bacterial motion enabled by flagella on the surface of semi-solid media. Swarming populations exhibit non-genetic or adaptive resistance to antibiotics, despite sustaining considerable cell death. Here, we show that antibiotic-induced death of a sub-population benefits the swarm by enhancing adaptive resistance in the surviving cells. Killed cells release a resistance-enhancing factor that we identify as AcrA, a periplasmic component of RND efflux pumps. The released AcrA interacts on the surface of live cells with an outer membrane component of the efflux pump, TolC, stimulating drug efflux and inducing expression of other efflux pumps. This phenomenon, which we call 'necrosignaling', exists in other Gram-negative and Gram-positive bacteria and displays species-specificity. Given that adaptive resistance is a known incubator for evolving genetic resistance, our findings might be clinically relevant to the rise of multidrug resistance.

Why chimpanzees carry dead infants: an empirical assessment of existing hypotheses

The study of non-human primate thanatology has expanded dramatically in recent years as scientists seek to understand the evolutionary roots of human death concepts and practices. However, observations of how conspecifics respond to dead individuals are rare and highly variable. Mothers of several species of primate have been reported to carry and continue to interact with dead infants. Such interactions have been proposed to be related to maternal condition, attachment, environmental conditions or reflect a lack of awareness that the infant has died. Here, we tested these hypotheses using a dataset of cases of infant corpse carrying by chimpanzees in Gombe National Park, Tanzania (n = 33), the largest dataset of such cases in chimpanzees. We found that mothers carried infant corpses at high rates, despite behavioural evidence that they recognize that death has occurred. Median duration of carriage was 1.83 days (interquartile range = 1.03-3.59). Using an information theoretic approach, we found no support for any of the leading hypotheses for duration of continued carriage. We interpret these data in the context of recent discussions regarding what non-human primates understand about death.

Differential Behavioral Responses of Solenopsis invicta (Hymenoptera: Formicidae) Workers Toward Nestmate and Non-Nestmate Corpses

The removal of corpses (aka 'necrophoric behavior') is critical to sanitation in ant colonies. However, little is known about differences in the necrophoric responses of Solenopsis invicta workers towards corpses of nestmates and non-nestmates. We introduced corpses of S. invicta workers from either intracolony (i.e., nestmate) or intercolony (i.e., non-nestmate) origin at the entrance of artificial nests, and recorded workers' aggressive responses and necrophoric behaviors for analysis. Solenopsis invicta workers displayed distinct responses towards corpses of different origins. Specifically, resident workers were more likely to remove fresh non-nestmate corpses than nestmate corpses, but there was no difference regarding corpses that had been dead for 15 min or longer. Resident workers reacted more aggressively to, and removed more quickly, fresh non-nestmate corpses than corpses of their nestmates. On the other hand, there was no significant difference in the removal time between nestmate and non-nestmate corpses that had been dead for 15 min or longer. Resident workers always displayed stronger aggressiveness towards non-nestmate corpses than nestmate corpses, excepting to corpses that had been dead for 6 h, which elicited a response. No significant correlation between the removal times and aggressiveness levels were detected in any treatments. It remains to be tested whether this differential response is adaptive in how it influences colony fitness and competition.

Cooperative policing behaviour regulates reproductive division of labour in a termite

Reproductive conflicts are common in insect societies where helping castes retain reproductive potential. One of the mechanisms regulating these conflicts is policing, a coercive behaviour that reduces direct reproduction by other individuals. In eusocial Hymenoptera (ants, bees and wasps), workers or the queen act aggressively towards fertile workers, or destroy their eggs. In many termite species (order Blattodea), upon the death of the primary queen and king, workers and nymphs can differentiate into neotenic reproductives and inherit the breeding position. During this process, competition among neotenics is inevitable, but how this conflict is resolved remains unclear. Here, we report a policing behaviour that regulates reproductive division of labour in the eastern subterranean termite, Reticulitermes flavipes. Our results demonstrate that the policing behaviour is a cooperative effort performed sequentially by successful neotenics and workers. A neotenic reproductive initiates the attack of the fellow neotenic by biting and displays alarm behaviour. Workers are then recruited to cannibalize the injured neotenic. Furthermore, the initiation of policing is age-dependent, with older reproductives attacking younger ones, thereby inheriting the reproductive position. This study provides empirical evidence of policing behaviour in termites, which represents a convergent trait shared between eusocial Hymenoptera and Blattodea.

Responses to death and dying: primates and other mammals

Although some definitions of thanatology-broadly definable as the study of death and dying-exclude nonhumans as subjects, recognition of the scientific value of studying how other species respond to sick, injured, dying and dead conspecifics appears to be growing. And whereas earlier literature was largely characterized by anecdotal descriptions and sometimes fanciful interpretations, we now see more rigorous and often quantitative analysis of various behaviors displayed towards conspecifics (and sometimes heterospecifics) at various stages of incapacitation, including death. Studies of social insects in particular have revealed chemical cues that trigger corpse management behaviors, as well as the adaptive value of these behaviors. More recent research on other taxonomic groups (including aquatic and avian species, and mammals) has sought to better document these animals' responses to the dying and dead, to identify influencing factors and underlying mechanisms, and to better understand the physiological, emotional, social and psychological significance of the phenomena observed. This special issue presents original short reports, reviews, and full research articles relating to these topics in New World monkeys, Old World monkeys and apes, as well as equids and proboscids. The range of events, data, hypotheses and proposals presented will hopefully enrich the field and stimulate further developments in comparative evolutionary thanatology.

Environmental decomposition of olefinic cuticular hydrocarbons of Periplaneta americana generates a volatile pheromone that guides social behaviour

Once emitted, semiochemicals are exposed to reactive environmental factors that may alter them, thus disrupting chemical communication. Some species, however, might have adapted to detect environmentally mediated breakdown products of their natural chemicals as semiochemicals. We demonstrate that air, water vapour and ultraviolet (UV) radiation break down unsaturated cuticular hydrocarbons (CHCs) of Periplaneta americana (American cockroach), resulting in the emission of volatile organic compounds (VOCs). In behavioural assays, nymphs strongly avoided aggregating in shelters exposed to the breakdown VOCs from cuticular alkenes. The three treatments (air, water vapour, UV) produced the same VOCs, but at different time-courses and ratios. Fourteen VOCs from UV-exposed CHCs elicited electrophysiological responses in nymph antennae; 10 were identified as 2-nonanone, 1-pentanol, 1-octanol, 1-nonanol, tetradecanal, acetic acid, propanoic acid, butanoic acid, pentanoic acid and hexanoic acid. When short-chain fatty acids were tested as a mix and a blend of the alcohols and aldehyde was tested as a second mix, nymphs exhibited no preference for control or treated shelters. However, nymphs avoided shelters that were exposed to VOCs from the complete 10-compound mix. Conditioned shelters (occupied by cockroaches with faeces and CHCs deposited on the shelters), which are normally highly attractive to nymphs, were also avoided after UV exposure, confirming that breakdown products from deposited metabolites, including CHCs, mediate this behaviour. Our results demonstrate that common environmental agents degrade CHCs into behaviourally active volatile compounds that potentially may serve as necromones or epideictic pheromones, mediating group dissolution.

2018 Highlights of Urban Entomology

The field of urban entomology is primarily associated with the study of ants, bed bugs, cockroaches, termites, and other occasional invader pests that are found within or near human-made structures. A wide array of peer-reviewed studies were published in 2018. The topics of these articles ranged from genomes and basic biology of urban insects to various applied aspects of pest management. Key findings of these papers are presented and discussed from the perspective of the contributions they make to the discipline of urban entomology. Additionally, potential future research opportunities that are evident from these publications have been outlined.

Evolutionary thanatology

Societies, including those of humans, have evolved multiple ways of dealing with death across changing circumstances and pressures. Despite many studies focusing on specialized topics, for example necrophoresis in eusocial insects, mortuary activities in early human societies, or grief and mourning in bereavement, there has been little attempt to consider these disparate research endeavours from a broader evolutionary perspective. Evolutionary thanatology does this by adopting an explicit evolutionary stance for studies of death and dying within the sociological, psychological and biological disciplines. The collection of papers in this themed issue demonstrates the value of this approach by describing what is known about how various nonhuman species detect and respond to death in conspecifics, how problems of disposing of the dead have evolved in human societies across evolutionary time and also within much shorter time frames, how human adults' understanding of death develops, and how it is ultimately reflected in death-related language. The psychological significance and impact of death is clearly seen in some species' grief-like reactions to the loss of attachment figures, and perhaps uniquely in humans, the existence of certain psychological processes that may lead to suicide. Several research questions are proposed as starting points for building a more comprehensive picture of the ontogeny and phylogeny of how organisms deal with death.This article is part of the theme issue 'Evolutionary thanatology: impacts of the dead on the living in humans and other animals'.

Corpse management of the invasive Argentine ant inhibits growth of pathogenic fungi

A dead conspecific poses a potential pathogen risk for social animals. We have discovered that Argentine ants (Linepithema humile) prevent spread of pathogenic fungi from corpses by depositing the dead to combined toilet and refuse areas and applying pygidial gland secretion on them. The presence of a corpse in a nest increases this secretion behaviour. We identified three fungi growing on Argentine ant corpses. Growth of the Argentine ant pathogen Aspergillus nomius and the plant pathogen Fusarium solani on corpses was inhibited as long as the ants were constantly attending them as the ant anal secretion only delayed germination of their spores. In contrast, the effect of the ant anal secretion on the human pathogen Aspergillus fumigatus was much stronger: it prevented spore germination and, accordingly, the fungus no longer grew on the treated corpses. The Argentine ants are one of the world's worst invasive alien species as they cause ecological and economical damage in their new habitats. Our discovery points at a novel method to limit Argentine ant colonies through their natural fungal pathogens.

Scent of death: Evolution from sea to land of an extreme collective attraction to conspecific death

All living organisms must eventually die, though in some cases their death can bring life-giving opportunities. Few studies, however, have experimentally tested how animals capitalize on conspecific death and why this specialization would evolve. Here, we conducted experiments on the phylogenetically most closely-related marine and terrestrial hermit crabs to investigate the evolution of responses to death during the sea-to-land transition. In the sea, death of both conspecifics and heterospecifics generates unremodeled shells needed by marine hermit crabs. In contrast, on land, terrestrial hermit crabs are specialized to live in architecturally remodeled shells, and the sole opportunity to acquire these essential resources is conspecific death. We experimentally tested these different species' responsiveness to the scent of conspecific versus heterospecific death, predicting that conspecific death would have special attractive value for the terrestrial species. We found the terrestrial species was overwhelmingly attracted to conspecific death, rapidly approaching and forming social groupings around conspecific death sites that dwarfed those around heterospecific death sites. This differential responsiveness to conspecific versus heterospecific death was absent in marine species. Our results thus reveal that on land a reliance on resources associated exclusively with conspecifics has favored the evolution of an extreme collective attraction to conspecific death.

Comparative thanatology, an integrative approach: exploring sensory/cognitive aspects of death recognition in vertebrates and invertebrates

Evolutionary thanatology benefits from broad taxonomic comparisons of non-human animals' responses to death. Furthermore, exploring the sensory and cognitive bases of these responses promises to allow classification of the underlying mechanisms on a spectrum from phylogenetically ancient to more derived traits. We draw on studies of perception and cognition in invertebrate and vertebrate taxa (with a focus on arthropods, corvids, proboscids, cetaceans and primates) to explore the cues that these animals use to detect life and death in others, and discuss proximate and ultimate drivers behind their capacities to do so. Parallels in thanatological behaviour exhibited by the last four taxa suggest similar sensory-cognitive processing rules for dealing with corpses, the evolution of which may have been driven by complex social environments. Uniting these responses is a phenomenon we term 'animacy detection malfunction', whereupon the corpse, having both animate and inanimate attributes, creates states of fear/curiosity manifested as approach/avoidance behaviours in observers. We suggest that integrating diverse lines of evidence (including the 'uncanny valley' effect originating from the field of robotics) provides a promising way to advance the field, and conclude by proposing avenues for future research.This article is part of the theme issue 'Evolutionary thanatology: impacts of the dead on the living in humans and other animals'.