Mimicry

Imagine that aliens secretly landed on Earth, kidnapped our political leaders and then masqueraded as those leaders. We would probably continue to lavish them with rewards and protection, even when their demands became excessive, because they would have all the outward signs of the powerful politicians they replaced. That is, they would all dress in drab power-suits and continue using the words to which we unthinkingly respond: freedom, happiness, fear, etc.

This may seem outlandish - at least the part about the aliens - but this is what happens when a certain species of caterpillar is adopted by an ant colony. Jeremy A. Thomas of the University of Oxford and colleagues discovered that the caterpillar fools worker ants into treating it like royalty by imitating the sounds produced by queen ants. Their work, published in Science, also demonstrates that merely playing back recordings of a queen ant causes the other ants to stand at attention, as if a queen were present.

A foreign species infiltrating ant colonies is nothing new. At least 10,000 invertebrates have evolved ways to exploit the robust social networks of ants. These social parasites, as they are called, often produce a chemical signal to trick the ants into taking care of them. In fact, the species of caterpillar featured in this study, Maculinea rebeli, secretes a chemical mimicking a compound covering the surface of ant larvae, compelling ants to feed them.

But, chemical mimicry alone is not sufficient to explain the incredible loyalty of ants to this impostor. For instance, the authors note that ants strongly prefer insect dummies coated with the authentic larval secretion to those coated with M. rebeli's imitation. But, when tested with live organisms, ants are more protective of M. rebeli than of their own larvae, even feeding their children to the caterpillar when food is scarce.

Thomas and colleagues hypothesized that perhaps M. rebeli was taking advantage of another ant communication system: stridulation. Stridulations are produced by rubbing a ridged surface, like dragging a spoon down a washboard. Both ants and caterpillars have a pair of organs, called the stridulatory file (the washboard) and the plectrum (the spoon), that produces these sounds.

Previous studies had suggested that queens might have different stridulation patterns than workers, raising the possibility that queens signal their status with stridulations. And, if so, that M. rebeli might pose as a queen using a similar sound pattern.

Sources

Barbero, Francesca, et al. "Queen Ants Make Distinctive Sounds That Are Mimicked by a Butterfly Social Parasite." Science, February 6, 2009, pages 782-785.

Bézier, Annie, et al. "Polydnaviruses of Braconid Wasps Derive from an Ancestral Nudivirus." Science, February 13, 2009, pages 926-930.