Saturniidae - Life Cycle

Life Cycle

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. 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 – e.g. the Luna Moth (Actias luna) or Callosamia securifera (both Saturniinae) –, spring and summer broods look different, with different genes activated by environmental conditions.

Eggs

Depending on the moth, a single female may lay up to 200 eggs on a chosen host plant. Others lay singly or in small groups. They are round, slightly flattened, smooth and translucent or whitish.

Larvae

Saturniid caterpillars are large (50 to 100 mm in the final instar), stout and cylindrical. Most have tubercules that are often also spiny or hairy. Many are cryptic in coloration, with countershading or disruptive coloration to reduce detection, but some are more colourful. Some have stinging hairs. A few species have been noted to produce clicking sounds with the larval mandibles when disturbed (e.g. Saturniini like Actias luna and Polyphemus Moth, Antheraea polyphemus). It has been hypothesized that the clicks serve as aposematic warning signals to a regurgitation defense. Most are solitary feeders, but some are gregarious. The Hemileucinae are gregarious when young and have stinging hairs, those of Lonomia containing a poison which may kill a human.

The other caterpillars in this size range are almost universally Sphingidae, which are seldom hairy and tend to have diagonal stripes on their sides. Many Sphingidae caterpillars bear a single curved horn on their hind end. These are actually not dangerous, but large haired caterpillars should generally not be touched except by experts.

Most saturniid larvae feed on the foliage of trees and shrubs. A few, particularly Hemileucinae such as Automeris louisiana, A. patagonensis and Hemileuca oliviae, feed on grasses. They moult at regular intervals, usually four to six times before entering the pupal stage. Prior to pupation there is a wandering stage, and the caterpillar may change colour, becoming more cryptic just before this stage.

Pupae

Most larvae spin a silken cocoon in the leaves of a preferred host plant or in leaf litter on the ground, or crevices in rocks and logs. While only moderately close relatives to the silkworm (Bombyx mori) among the Lepidoptera, the cocoons of most larger saturniids can be gathered and used to make silk fabric. However, larvae of some species – typically Ceratocampinae, like the Regal Moth (Citheronia regalis) and the Imperial Moth (Eacles imperialis) – burrow and pupate in a small chamber beneath the soil. This is common in the Ceratocampinae and Hemileucinae. Unlike most silk moths, those that pupate underground do not use much silk in the construction. Once enclosed in the cocoon, pupae undergo metamorphosis.

Adults

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.

Since the mouthparts of adult saturniids are vestigial and digestive tracts are absent, 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 once emerged from the pupa.