A very large family of small to medium sized moths characterised by larvae having only two functional hind claspers and drawing the body up to the thoracic legs on movement, giving rise to the common names of "loopers" or "inch worms". Larvae are often very procryptic, resembling twigs or stems but others are internal feeders in seed heads and a few make silken spinnings in leaves. The imagines are slim bodied with relatively broad wings evolved for low speed flight and many often flying in evenings and at dusk but also some species are strongly attracted to light. Some are diurnal and fly in sunshine and many can be disturbed in the day. Often rest by day on tree trunks, walls and rocks or under leaves with wings spread out horizontally, and this posture is particularly marked in the "pugs" and "waves". Some species that fly early in the spring or later in the autumn or winter, have flightless females with vestigial wings.