Trophallaxis

Trophallaxis is a social feeding behavior in which one animal directly transfers liquid food or other fluid material to another animal. The very term ‘trophallaxis’ derives from the Greek words trophé, meaning ‘nourishment,’ and allaxis, meaning ‘exchange’.¹ This behavior is commonly observed in eusocial insects, such as ants, termites, and bees, though some solitary insects, such as burying beetles, also exhibit trophallaxis in certain stages of their life cycle.²

There are 2 types of trophallaxis: stomodeal and proctodeal. In stomodeal trophallaxis, the transfer of material happens mouth-to-mouth, whereas in proctodeal trophallaxis, the transfer takes place anus-to-mouth. While stomodeal trophallaxis is the more familiar form and is typically observed in ants, bees, and wasps, proctodeal trophallaxis is found in termites and wood-feeding cockroaches.

Why Animals Use Trophallaxis

Highly social insects typically live in large colonies that function cooperatively through the division of labor. When a forager has already collected food material, it simply passes it on to other colony members that do not collect food themselves, such as larvae, queens, nurse workers, or other non-foraging adults. Through this constant relay of food, resources are spread throughout the colony, sparing any single individual from having to put in all the effort.

How Trophallaxis Works

In stomodeal trophallaxis, the donor first collects or stores liquid food in its body. Many ants and bees have a specialized sphincter, the proventriculus, that separates the crop (an expandable part of the digestive tract before the stomach) from the midgut, where the digestion actually takes place.³

The transfer is initiated when the donor makes contact with the receiver, typically through their mouthparts, such as mandibles. During the interaction, the donor regurgitates stored food from its crop, only partially emptying it, and passes it on to the receiver.

In proctodeal trophallaxis, instead of collecting food from another animal’s mouth, the receiver takes it in from the donor’s rectal region.

Trophallaxis Across Animals

Although trophallaxis is observed most often in social insects, some vertebrates also exhibit trophallaxis-like food transfer, especially when adults regurgitate food to young or share food with their social partners.

Animal Group	What is Transferred	Trophallaxis Type
Ants	Liquid food, sometimes social-fluid materials	Stomodeal
Bees	Nectar or liquid food	Stomodeal
Wasps	Liquid food	Stomodeal
Termites	Hindgut fluid with digestive microbes	Proctodeal
Birds	Regurgitated food or crop secretions	Stomodeal
Wolves	Regurgitated meat	Stomodeal
Vampire Bats	Regurgitated blood	Stomodeal

Tradeoffs

Despite its importance in social groups, trophallaxis has its own disadvantages. Since it involves close contact and fluid transfer among animals, it may also make way for pathogens and parasites to enter their colonies. Moreover, it also does not guarantee equal sharing among the group members.

In some species, such as the parasitic yellowjacket (Vespula infernalis), social parasites can invade a host colony and exploit the food being shared through trophallaxis. A parasitic female typically enters the nest of another Vespula species and removes or suppresses the host queen, taking over the role of the primary reproductive female in the nest. As the new queen, the parasite then takes advantage of the trophallaxis system by forcing the workers to share the food with her. The food that would normally support the host colony is thereby redirected toward the parasite.⁶