Characteristics of Giant Silkworm Moths and Royal Moths

Cecropia moth on a tree trunk

Darrell Gulin / Getty Images

Even people with no particular love of insects find the giant moths (and caterpillars) of the family Saturniidae fascinating. The name is thought to refer to the large eyespots found on the wings of some species. The eyespots contain concentric rings, reminiscent of the planet Saturn's rings. These showy moths are easy to rear in captivity if you can find enough foliage to keep their very hungry caterpillars fed.

Physical Characteristics

Among the Saturniids, we find the largest moth species in North America: the luna moth, the cecropia moth, the polyphemus moth, the imperial moth, the io moth, the Promethea moth, and the royal walnut moth. The cecropia moth is a giant among giants, with the longest wingspan—a remarkable 5-7 inches—of all. Some Saturniids may seem dwarf-like compared to their gigantic cousins, but even the smallest of the wild silkworm moths measures a respectable 2.5 cm in wide.

Giant silkworm moths and royal moths are often brightly colored, which may mislead first-time observers to refer to them as butterflies. Like most moths, however, Saturniids hold their wings flat against their bodies when at rest, and usually have stout, hairy bodies. They also bear feathery antennae (often bi-pectinate in form, but sometimes quadri-pectinate), which are quite conspicuous in males.

Saturniid caterpillars are hefty, and often covered with spines or protuberances. These tubercles give the caterpillar a threatening look, but in most cases, they're quite harmless. Do beware of the io moth caterpillar, though. Its branched spines pack a painful dose of venom and will inflict a long-lasting sting.


  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Class: Insecta
  • Order: Lepidoptera
  • Family: Saturniidae


Adult silkworm and royal moths don't feed at all, and most have only vestigial mouthparts. Their larvae, however, are a different story. The largest caterpillars in this group can exceed 5 inches in length in their final instar, so you can imagine how much they eat. Many feed on common trees and shrubs, including hickories, walnuts, sweetgum, and sumac; some can cause significant defoliation.

Life Cycle

All giant silkworm moths and royal moths undergo complete metamorphosis with four life stages: egg, larva, pupa, and adult. In the Saturniids, an adult female may lay several hundred eggs during her brief lifetime, but perhaps only 1% will survive to their own adulthood. This family overwinters in the pupal stage, often in silken cocoons joined to twigs or nestled in a protective envelope of leaves.

Special Adaptations and Behaviors

Female Saturniid moths invite males to mate by releasing a sex pheromone from a special gland at the end of their abdomens. The male moths are renowned for their determination and unwavering focus on the task of locating the receptive female. They have a keen sense of smell, thanks to their feathery antennae brimming with sensilla. Once a male giant silkworm moth catches a whiff of a female's scent, he will not be deterred by foul weather, nor does he let physical obstacles impede his progress. A Promethea moth male holds the long-distance record for following a female's pheromones. He flew an incredible 23 miles to find his mate!

Home Range

References vary greatly in their accounting of how many Saturniid species live worldwide, but most authors seem to accept a number in the range of 1200-1500 species. About 70 species inhabit North America.


  • Family Saturniidae - Giant Silkworm and Royal Moths, Accessed January 10, 2013.
  • Saturniidae, Butterflies and Moths of North America. Accessed January 10, 2013.
  • Saturniid Moths, University of Kentucky Entomology. Accessed January 10, 2013.
  • The Wild Silk Moths of North America: A Natural History of the Saturniidae of the United States and Canada, by Paul M. Tuskes, James P. Tuttle, and Michael M. Collins.
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Hadley, Debbie. "Characteristics of Giant Silkworm Moths and Royal Moths." ThoughtCo, Aug. 27, 2020, Hadley, Debbie. (2020, August 27). Characteristics of Giant Silkworm Moths and Royal Moths. Retrieved from Hadley, Debbie. "Characteristics of Giant Silkworm Moths and Royal Moths." ThoughtCo. (accessed March 27, 2023).