Hook-tip moth caterpillars are noisy houseguests and, it turns out, quiteÂ territorial.
The hook-tip moth caterpillar's territorial behavior is much like that of many vertebrates, not what you'd expect in an organism like a caterpillar. These caterpillars find themselves a good leaf, and then they construct a nest of silk to protect them while they feast. When another caterpillar intrudes upon the resident caterpillar's territory, the resident caterpillar stops eating, retreats into its nest and it makes tapping noises by dragging or striking its mandibles against the leaf.
Often the intruder makes the sound as well and may end up attacking the resident's nest by biting through some of the silk strands. Caterpillars don't make this noise anywhere but in the nest, and scientists say this behavior suggests that the rivals are sizing each other up. The sounds may also result in attracting the attention of predators, in which case the intruder would be rather defenseless.
"Caterpillars Make Noise To Fend Off Intruders, Researchers Discover" (Science Daily)