Trophallaxis

Formica obscuripes

Trophallaxis- the social sharing of regurgitated liquids- is a fundamental behavior in the biology of most ant colonies.  One ant approaches another, asks for a droplet of food, and if her partner is willing the two spend anywhere from a few seconds to several minutes in what is best described as a myrmecological french kiss.  The behavior is so central to the life of ants that the insects have an entire stomach, separate from their digestive gut, devoted as a reservoir for social sharing.

Although the act involves a transfer of food, it would be a mistake to think of the behavior as primarily a nutrient-dispersal mechanism. Ants do it far more frequently than nutrition requires.  Trophallaxis also transfers chemical signals among nestmates, regulating a singular colony odor and sharing information about the needs of the colony. Think of it as the colonies' own internet.

Over the weekend I set out to rectify my rather embarrassing lack of decent trophallaxis photographs. We have a laboratory colony of Formica obscuripes that are ideal subjects, as these large ants are not only charismatic but engage in trophallaxis with what seems to be a nearly pathological frequency.  Here are a few of the better shots.

To capture this series, I borrowed a technique from Benoit Guenard.  I set a tall tupperware container inside the open, fluon-lined plastic tub housing a large and active laboratory ant colony.  A 6" square of white paper affixed to the top of the tupperware created a plain white platform.  In essence, I made a raised stage that allowed for photographing the ants in side view while still retaining them in their escape-proof nest.

Once the ants accept the structure they behave relatively normally on it, as if the platform were a natural extension of their territory.  A drop of honey water entices them to feed, followed minutes later by a predictable cascade of trophallaxis.