some species of caterpillars (in the family lycaenidae) are tended by ants. the caterpillars have special glands that make a sweet liquid called honeydew. the ants like the honeydew. in return for the honeydew, the ants protect the caterpillars from predators. the caterpillars also have special body parts that make sounds. the caterpillar will make sounds with the body parts and "call" the ants when the caterpillar is being attacked by predators. the ants hear the sounds and come to protect the caterpillar.