The caterpillars of some saturniid moths are infamous tree pests. The rosy maple moth, for example, periodically has outbreaks that can sometimes completely defoliate soft maple trees. Generally, and over the long term, these caterpillars do not cause serious harm to their tree hosts.
Moths, in all stages of life, are food for many kinds of predators. The forewings of many saturniids provide them camouflage against the leaves and trunks they commonly perch on. The hindwings of several (such as the polyphemus and io) have large, conspicuous eyespots, which the moth, when disturbed, will reveal by sliding its forewings sideways. The sudden, startling sight of owl-like eyes may make a predator hesitate long enough for the moth to fly away to safety.
The stinging or irritating hairs or spines on the caterpillars of many species is a reminder that these large, juicy larvae would otherwise be choice morsels for many kinds of predators. Doubtless many predators — owls, perhaps, and snakes — are unfazed by the noxious hairs and spines.
There are several other defense mechanisms among members of this family. The caterpillars of some make clicking noises and vomit to deter predators. The tails on the hindwings of luna moths apparently disrupt the sonar that hunting bats use to locate the moths.
Populations of our native saturniid moths are shrinking as an unanticipated result of fly and wasp parasites intentionally introduced to North America to prey on nonnative, invasive gypsy moths. People concerned with the devastation caused by gypsy moth caterpillars identified insect parasitoids from the gypsy moth’s native lands and introduced them to America. Unfortunately, those parasitoids also attack several of our native saturniids, including cecropia, luna, and promethea moths, reducing their populations in New England and elsewhere. Meanwhile, those parasitoids have not ended the threat of the gypsy moth. The harmful effects on nontarget species are critical issues in combating invasive plants and animals.