Ant nests are rich sources of food, which is probably why thousands of parasites have evolved methods of infiltrating ant societies. Jeremy Thomas (University of Oxford, UK) and coworkers have found that a parasitic caterpillar induces worker ants to treat them like a queen ant by mimicking their vocalizations.
How did this theory come about?
Maculinea rebeli is a well-studied parasitic caterpillar. These parasites secrete chemicals to trick worker Myrmika schencki ants into believing that they are ant larvae, in order to get fed by the ants.
However, this use of chemical mimickry does not explain why workers treat the parasites as they do the queen. The parasites are rescued by the worker before ant larvae if the nest is disturbed.
Workers will kill other workers to feed the parasites, if food is scarce. Furthermore, queens treat the parasites like rivals, while workers treat the parasites like queens.
The scientists hypothesized that vocalizations by the parasite may be responsible. They then set out to test this hypothesis.
The first test was whether or not ants use vocalizations to distinguish social status. The second test was whether or not the parasites mimic these vocalizations to trick workers into believing that they are queens.
Ants vocalize to distinguish social status.
Ant vocal communication is generally thought to be less important than chemical communication. However, recent research suggests that their vocal communication may be underappreciated.
The scientists discovered that the vocalization organ of the queen is 44% longer than that of the workers, and possesses a 33% wider gap between the ridges of the organ. This suggests that queen vocalizations may be different from worker vocalizations.
The scientists then recorded the sounds emitted by the queens and workers. They found that although their pulse lengths and repetition frequencies were similar, their dominant frequency and overall acoustics were quite different.
The scientists played these sounds on miniature speakers to workers, and the workers responded to it as they would an ant. Furthermore, playing queen sounds were more likely to induce the workers to stand on guard; in other words, stand motionless in a specific posture reserved for while attending queens.
Parasites mimic queen vocalizations.
This demonstrates that ants use vocalizations to establish social heirarchy. Do the parasites take advantage of this behavior?
Caterpillar pupae and larvae emit vocalizations from a different organ than the ants. However, the vocalizations were 23% (pupae) and 27% (larvae) closer to those of the queens than the workers.
The scientists then played these sounds to workers, similarly to the previous experiments. Similar on guard posturing was observed.
How the parasites infiltrate ant societies.
The scientists suggest that the parasitic caterpillars are initially brought into the ant society through chemical trickery (pretending to be ant larvae). Later, they achieve elevated status through vocal trickery (pretending to be the queen).
It is unknown if this behavior is exhibited by other parasites, but it stands to reason that if it has evolved once, it has also evolved elsewhere. Insect societies are very complex; we may be just beginning to understand how they function, and how they can be manipulated by others.
for more information:
Barbero, F.; Thomas, J. A.; Bonelli, S.; Balletto, E.;
Schönrogge, K.
Queen ants make distinctive sounds that are mimicked by a
butterfly social parasite.
Science 2009, 323, 782-785.