The Saturniidae, collectively known as saturniids, are among the largest and most spectacular of the Lepidoptera (or moths), with an estimated 1,200 to 1,500 different species existing worldwide. These moths are often brightly colored and have translucent eyespots on their wings to frighten predators. Sexual dimorphism varies by species, but males can always be distinguished by their larger, broader antennae. Most adults possess wingspans between 1 to 6 inches (2.5 to 15 cm), but some tropical species, such as the atlas moth (Atticus atlas), may boast incredible wingspans of up to 12 inches (30 cm).
The Saturniidae family includes the giant silkmoths, royal moths, and emperor moths.
Though they are found worldwide, the majority of saturniid species occur in wooded tropical or subtropical regions. There are approximately one dozen described species living in Europe, one of which, the Emperor Moth, occurs in the British Isles, and 68 described species living in North America, 42 of which reside north of Mexico.
Saturniid larvae come in a variety of shapes, sizes, and colors – they may be smooth, fuzzy, or covered with tubercles or spines. All larvae feed on the foliage of trees and shrubs. They molt at regular intervals, usually four to six times before entering the pupal stage.
Most larvae spin a silken cocoon in the leaves of a preferred host plant or in leaf litter on the ground. However, larvae of the regal moth (Citheronia regalis) and imperial moth (Eacles imperialis) burrow and pupate in a small chamber beneath the soil.
Some saturniids produce 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 that day length during the larvae’s 5th instar plays a major role. Longer days may prompt pupae to develop early, while shorter days result in pupal diapause.
Once enclosed in the cocoon, pupae undergo metamorphosis.
Adult females emerge with a complete set of mature ova and “call” males by emitting pheromones (specific “calling” times vary by species). Males can detect these chemical signals up to a mile away with help from sensitive receptors located on the tips of their featherlike antennae. The males will fly several miles in one night to locate a female and mate with her; females generally will not fly until after they have mated.
Depending on the moth, a single female may lay up to 200 eggs on a chosen host plant.
Unlike most lepidoptera, saturniids employ a synchronized breeding strategy in which adult moths do not spend time to feed. Mouthparts are vestigial and digestive tracts are absent; instead, adults subsist on stored lipids acquired during the larval stage. As such, adult behavior is devoted almost entirely to reproduction, but the end result (due to lack of feeding) is a lifespan of a week or less.