Saturniidae, commonly known as saturniids, is a family of Lepidoptera with an estimated 2,300 described species. The family contains some of the largest species of moths in the world. Notable members include the emperor moths, royal moths, and giant silk moths. Adults are characterized by large, lobed wings, heavy bodies covered in hair-like scales, and reduced mouthparts. They lack a frenulum, but the hindwings overlap the forewings to produce the effect of an unbroken wing surface. Saturniids are sometimes brightly colored and often have translucent eyespots or "windows" on their wings. Sexual dimorphism varies by species, but males can generally be distinguished by their larger, broader antennae. Most adults possess wingspans between 1-6 in (2.5–15 cm), but some tropical species such as the Atlas moth (Attacus atlas) may have wingspans up to 12 in (30 cm). Together with certain Noctuidae, Saturniidae contains the largest Lepidoptera and some of the largest insects alive today. Distribution The majority of saturniid species occur in wooded tropical or subtropical regions, with the greatest diversity in the New World tropics and Mexico, though they are found all over the world. About 12 described species live in Europe, one of which, the emperor moth, occurs in the British Isles, and 68 described species live in North America, 42 of which reside north of Mexico and Southern California. Life cycle Some saturniids are strictly univoltine, producing only one generation a year, whereas others are multivoltine, producing more than one brood a year. Spring and summer broods hatch in a matter of weeks; autumn broods enter a state known as diapause and emerge the following spring. How the pupae know when to hatch early or hibernate is not yet fully understood, though research suggests day length during the fifth larval instar plays a major role, as well as cooling temperatures. Longer days may prompt pupae to develop early, while shorter days result in pupal diapause. The number of broods is flexible, and a single female may produce both fast-developing and slow-developing individuals, or they may produce different numbers of broods in different years or parts of the range. In some species, the spring and summer broods look different from each other; for example, the two Saturniinae species Actias luna (the Luna moth) and Callosamia securifera both have certain genes which may or may not be activated depending upon differences in environmental conditions. Eggs Depending on the moth, a