thumb|300px|right|Trophallaxis in Asian-Australian [[weaver ant O. smaragdina, Thailand]]
Trophallaxis () is the direct transfer of fluid and food (excreted, secreted or regurgitated) between individuals, typically through mouth-to-mouth (stomodeal) or anus-to-mouth (proctodeal) feeding. Along with nutrients, trophallaxis can involve the transfer of molecules such as proteins, hormones, organisms such as symbionts, and information to serve as a form of communication. Trophallaxis is used by some birds, gray wolves, vampire bats, and is most highly developed in eusocial insects such as ants, and termites. Like lactation, trophallaxis transmits socially transferred materials between bodies.
Etymology
Trophallaxis is derived from Greek trophé, meaning 'nourishment' and allaxis, meaning 'exchange'. The word was introduced by the entomologist William Morton Wheeler in 1918. Wheeler's original conception was much broader than often recognized. He described the evolution of trophallaxis as an "ever-widening vortex" that began as a mutual trophic relation between parent and offspring but expanded to encompass increasingly complex relationships.
Evolutionary significance
Phylogenetic analyses show that trophallaxis has played a major role in evolutionary diversification within ants. Trophallaxis evolved in ant lineages around 130 and 90 million years ago, coinciding with the rise of flowering plants that provided new liquid food sources like nectar and honeydew. Lineages that evolved trophallaxis showed higher net diversification rates compared to non-trophallactic lineages. appears to have been a key innovation that contributed to the ecological dominance of this major social insect lineage, facilitating efficient resource distribution, large colony sizes, high dimorphism between queens and workers, and sophisticated division of labor across thousands of individuals.
Trophallaxis was used in the past to support theories on the origin of sociality in insects. The Swiss psychologist and entomologist Auguste Forel also believed that food sharing was key to ant society and he used an illustration of it as the frontispiece for his book The Social World of the Ants Compared with that of Man. Proctodeal trophallaxis allowed termites to transfer cellulolytic flagellates that made the digestion of wood possible and efficient. Besides sociality, trophallaxis has evolved within many species as a method of nourishment for adults and/or juveniles, kin survival, transfer of immunity, colony recognition and foraging communication. Trophallaxis has even evolved as a parasitic strategy in some species to obtain food from their host. Trophallaxis can also result in the spreading of chemicals, such as pheromones, throughout a colony, which is significant in social colony functioning.
Species have evolved anatomy to allow them to participate in trophallaxis, such as the proventriculus in the crops of Formica fusca ants. These birds have evolved brightly coloured gapes that stimulate the host to transfer food. Trophallaxis serves as a means of communication, at least in bees, like M. genalis, and ants. Trophallaxis in M. genalis is part of a social exchange system, where dominant bees are usually the recipients of food. This is because cooperation among non-relatives offers more benefit than cost to the group. This bee species allows one adult to forage and bring nectar back for the rest of the nest population as a way to continually defend the nest while obtaining nutrients for all members of the colony. Transfer of gut symbionts in these species is essential to digest wood as their food source. Carpenter ants transfer immunity through trophallaxis by the direct transfer of antimicrobial substances, increasing disease resistance and social immunity of the colony. though this has been debated., but the significance of this network remains unknown.
In addition, Vespula austriaca wasps also engage in trophallaxis as a form of parasitism with its host to obtain nutrients. V. austriaca is an obligate parasite species that invades the nests of host species and obtains food by constraining the host with their legs and forcing trophallaxis.
Wild wolves transport food in their stomach to pups and/or breeding females and share it by regurgitation, as a form of trophallaxis. The recipient wolves often lick or sniff the donor wolf's muzzle to activate regurgitation and receive nutrients. The cuckoo brood parasite is another bird species that engages in trophallaxis. The cuckoo bird uses mimicry, such as mimicking the eggshell colors and patterns of the host's eggs, to place their young in the nest of host species where they will be fed and reared at no expense to the cuckoo mother.