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|Male Small Emperor Moth, Saturnia pavonia (Saturniinae)|
|Male Small Emperor Moth, Saturnia pavonia (Saturniinae)|
The Saturniidae, commonly known as saturniids, are among the largest of the moths. They form a family of Lepidoptera, with an estimated 2,300 described species worldwide. The Saturniidae include such Lepidoptera as the giant silkmoths, royal moths and emperor moths.
Adults are characterized by large size, heavy bodies covered in hair-like scales, lobed wings, reduced mouthparts, and small heads. They lack a frenulum but the hind wings overlap the forewings, producing the same effect of an unbroken wing surface. These moths 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 to 6 inches (2.5 to 15 cm), but some tropical species, such as the Atlas Moth (Attacus atlas), may have wingspans of up to 12 inches (30 cm). Together with certain Noctuidae (chiefly Calpinae and Catocalinae, such as the genera Ascalapha, Erebus or Thysania), the Saturniidae contain the largest Lepidoptera, and some of the largest insects alive today.
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. 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 and Southern California.
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.
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. A. armida is another well-known example, and are infamous for their large conspicuous masses during the day. Their coloration is not cryptic, instead exhibiting aposematism.
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.
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.
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.
A few species are important defoliator pests, including the Orange-striped Oakworm Moth (Anisota senatoria) on oaks, the Pandora Pinemoth (Coloradia pandora) on pines and Hemileuca oliviae on range grasses.
Other species are of major commercial importance in tussah and wild silk production. These notably include the Chinese Tussah Moth (Antheraea pernyi), its hybridogenic descendant Antheraea × proylei, and the Ailanthus Silkmoth (Samia cynthia). However, the corn earworm moth is a major agricultural pest.
Many species of Saturniidae are a valuable food source for man in sub-Saharan Africa, examples being the Mopane Worm (Gonimbrasia belina), Gonimbrasia zambesina, the Cabbage Tree Emperor Moth (Bunaea alcinoe), Gynanisa maia, Imbrasia epimethea, Imbrasia oyemensis, Melanocera menippe, Microgone cana, Urota sinope and the Pallid Emperor Moth (Cirina forda).  
Most Saturniidae are harmless animals at least as adults, and in many cases at all stages of their life. Thus, some of the more spectacular species – in particular Antheraea – can be raised by children or school classes as educational pets. The soft, silken cocoons make an interesting keepsake for pupils.
In terms of absolute numbers of species, the Saturniidae most diverse in the Neotropics. Also, their most ancient subfamilies occur only in the Americas. Only the very "modern" Saturniidae are widely distributed across most parts of the world. Thus, it is quite safe to assume – even in the absence of a comprehensive fossil record – that the first Saturniidae flew around in the neotropical region.
The following list arranges the subfamilies in the presumed phylogenetic sequence, from the most ancient to the most advanced one. Some notable genera and species are also included.
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