Moths constitute one of the most diverse and abundant groups of insects globally and are richly represented in nearly every terrestrial habitat. The most distinctive feature of adult moths and butterflies is the dense, colorful scaling covering nearly the entire body. Moths and butterflies undergo complete metamorphosis, with four distinct life stages: egg, larva, pupa, and adult. The larva, which has up to several pairs of prolegs in addition to three pairs of true legs, is usually called a caterpillar; it produces silk used to build shelters and hang from foliage. In many species, the larva spins a silken cocoon and pupates within it. Adults have two pairs of wings, though these are reduced or absent in females, and more rarely in males, of some species.

Moths and butterflies comprise the order Lepidoptera, one of the four largest insect orders along with Coleoptera (beetles), Diptera (flies), and Hymenoptera (wasps and bees), with over 150,000 described species. In phylogenetic terms, butterflies are one diverse clade of moths; their most recent common ancestor was a moth. Butterflies are usually considered separately from the rest of Lepidoptera (i.e. “moths”) for historical and practical reasons: the adults are exclusively diurnal and by far the most conspicuous and abundant day-flying Lepidoptera. (This division in common names is not reflected in all languages; in French, for instance, all Lepidoptera are papillons.) Butterflies’ diurnal habits, heavy reliance on nectar for food, and vibrant colors in their adult stage have made them the most popular and best-studied group of insects. However, butterflies have not been a focus of the Block Island moth survey due to the popular distinction between them and the rest of Lepidoptera; their already being very well-studied; and, crucially, their diurnal habits, which mean they can’t be studied by surveying with lights.