One of the most interesting aspects of life in a
social insect colony is the exchange of liquid foods between
colony members. The process is known as trophallaxis, a term coined by W. M. Wheeler in
1918. Trophallaxis has many separate functions in different insect species. More than just an exchange of nutrients, it is a method of communication and recognition, of maintaining the colony's signature odor, and of transferring symbionts of vital importance. Studies have shown that trophallaxis can even be used between colonies, and even between species, as a method of appeasing aggressors.
The most obvious form of trophallaxis, and the only form that has a parallel in vertebrate life, is the passing of food to colony members that are incapable of finding their own food. Most commonly this consists of adults passing food to the nymphs and queens. However, in some species the larvae actually do the processing of all the food, transforming it into carbohydrates for return to the adults.
Important symbionts are also transferred through trophallaxis. Many termites transfer "proctodeal food" from their hindguts through anal trophallaxis. This substance contains the symbiont flagellates that help the termites digest cellulose. These symbionts are lost every time a nymph molts, and must be replaced through trophallaxis.
Trophallaxis is performed by every member of the colony, on a relatively equal basis depending on the satiation level of the individual. As soon as an insect becomes hungry it will begin to solicit trophallaxis from every other colony member that approaches it. Contact is made by stroking the prospective donor's mouth with the antennae. This seems to transmit both a tactile and chemical signal. Interestingly, the cue system favours larger individuals. Dominant insects such as queens and larger workers tend to receive much more than they give.
Insects that are fully satiated will begin to give more than they receive, with the result that food is distributed as equally as possible throughout the colony. Experiments have shown that within one day of feeding a single worker ant honey mixed with a marking substance, particles of the marker will be found in the stomachs of every member of the colony. Within a short period the marked food will be nearly equally distributed throughout the colony. Because of the frequency of exchange, entomologists sometimes refer to a "communal stomach" consisting of the crops of every adult member of the colony.
Sources:
- "Insect Behavior", Matthews & Matthews 1978.
- http://aci.mta.ca/Courses/Biology/3401/The%20Final%20Reward!/Hamid:Chisholm/trophallaxis/function.html
- http://www.main-kinzig.net/privat/MartinHallmen/seite75.htm
- http://sundoc.bibliothek.uni-halle.de/diss-online/98/98H133/t6.pdf