Thisbe irenea

Thisbe irenea is a butterfly whose caterpillar turns ants into unusually responsive bodyguards through a combination of signals and secretions. Its methods make the caterpillar a striking example of the extended phenotype: genes can influence the behaviour of an organism in another body, redirecting that organism’s actions toward the genes’ propagation.

Identity and protective relationship

The caterpillar lives in an ants’ nest and uses ants for protection. Like aphids, which rely on ants’ ordinary aggression against predators, it benefits from the ants’ defensive capacity. But it goes beyond recruiting existing behaviour: the caterpillar can alter how its protectors respond to their surroundings.

Signals and chemical manipulation

The caterpillar has a sound-producing organ in its head that summons ants and a pair of telescopic spouts near its rear end that release attractive nectar. A further pair of nozzles on its shoulders secretes a volatile substance. The secretion appears not to be food; instead, it changes the ants’ behaviour. An ant under its influence leaps clear, opens its jaws, and becomes more eager than usual to attack, bite, or sting moving objects—while leaving the caterpillar itself alone.

Binding and extended effects

The manipulation can persist: an affected ant may enter a state described as binding, remaining inseparable from the caterpillar for many days. The caterpillar thus combines a call, a food reward, heightened aggression, and prolonged attachment. Its protection is not simply the incidental result of ants behaving as they normally do; the account presents the caterpillar as actively shifting their behaviour in ways that benefit it.

This example belongs to a wider account of parasites and other organisms influencing their hosts. In that framework, the key question is not merely whether an animal’s behaviour benefits the genes in its own body, but whose genes the behaviour benefits. The caterpillar’s effects on its ant protectors make that question concrete: genes can have phenotypic effects beyond the body in which they reside, even when the manipulated organism belongs to another species.