The Lycaenids are a group of butterflies known commonly as blues, coppers and hairstreaks. Most species of Lycaenid butterflies have evolved close, mutually- beneficial relationships with different species of ants.
A Special Relationship
The caterpillars of these butterflies develop special glands that secrete a nectar-like substance to attract ants. The ants swarm all over the caterpillars, drinking the secretion. The ants "milk" secretions from the caterpillars by tickling special glands on the caterpillars with their antennas.
In some Australian species, the attending ants even build thatched or earthen corrals to contain the caterpillars. By day the caterpillars are protected from predators by the corral and the ants. At night the ants herd the caterpillars up a nearby tree to feed on leaves.
What Do The Caterpillars Get Out Of It?
The ants are like a private army of bodyguards. Colonies of ants are quite fierce - swarming, biting or even consuming potential predators.
In fact, the caterpillars' sweet secretions are not only nutritious, but also contain chemicals that subdue the ants. Otherwise the ants might kill the caterpillars themselves! Some caterpillars also make drumming sounds to keep their attendant ants alert.
Unprotected caterpillars would make a tasty treat for insect-eaters like birds, frogs or larger insects. But ants taste bitter or even toxic when eaten. To most predators, a caterpillar covered in ants is about as appetizing as a candy bar covered in thumbtacks.
So, the ants benefit from the energy-rich secretions produced by the caterpillars, and the caterpillars benefit from the ants' protection.