Giant Silk Moths in North America

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iant silk moths are large moths placed in the Saturniidae family. Sometimes called giant silkworm moths, these beauties are the largest moths in temperate North America and are truly spectacular. Silk moths often have dazzling colors and amazing eye spot patterns on their wings. The caterpillars are also stunning; they are usually large and beautifully colored with knobs or spines. One of the most well-known giant silk moths in eastern North America is probably the Luna moth.

I live in the Northeast and have seen all of the giant silk moth species present in this area. Below you will find an introduction to the life history traits of these insects, a description with photos of the silk moths in eastern / east-central North America, and links for more information about these amazing moths.

A brief introduction to life history traits

Before we go any further we need to understand just what a moth is and how they compare to butterflies, which are a close relative.

Both moths and butterflies belong to the Order Lepidoptera, however, moths are much more common than butterflies and there are about ten times more moth species worldwide. Like many insects, there are still countless moth species yet to be described (scientifically). Moths and butterflies are closely related and the consensus among entomologists is that butterflies evolved from moths into a separate group.

One of the basic differences between butterflies and moths is activity and feeding. The vast majority of moths are nocturnal (active at night) or crepuscular (active at dawn and dusk) whereas butterflies are almost always diurnal (active during the day). Both moths and butterflies mainly feed on nectar.

Giant silk moths have no mouth parts and therefore cannot eat. As such the average lifespan for an adult giant silk moth is only around two weeks.

Giant silk moths undergo a developmental process called complete metamorphosis. This is the traditional metamorphosis in which the insect has distinct phases: egg, larva, and adult. A single female giant silk moth is capable of laying hundreds of eggs onto a specific/preferred host plant. Many of the caterpillars which hatch will be eaten by birds or fall victim to parasites. The surviving caterpillars will go though a total of four different instars. An instar is a developmental stage; in order to grow a caterpillar must shed its exoskeleton and each shedding results in another instar. Once a caterpillar has fed and stored enough energy for its development it will spin a silken cocoon (usually attached to a branch) and overwinter. Most silk moths emerge from their cocoons with the first early summer heat wave.

Larvae or caterpillar

Photo: courtesy Wikimedia Commons

Adult moth

Photo: courtesy Wikimedia Commons

This species is North America's largest native moth! Females with wingspans of 160mm or larger have been documented. Its range reaches as far west as the Rockies and extends Northward into the maritime provinces of Canada. The cecropia moth larvae commonly feed on maple and ash, although they have been found a variety of other plants.

Larvae or caterpillar

I took this photograph, my brother located the caterpillar.

Adult moth

Photo courtesy Wikimedia Commons

This species has an average wingspan of 15 cm (6 inches). The large eye spots on the hind wings of these moths are its most notable feature. Amazingly, the polyphemus caterpillar is capable of eating 86,000 times its hatching weight in less than two months! It can be found throughout North America from southern Canada to Mexico.

Larvae or caterpillar

Photo: Wikimedia Commons

Adult moth

Photo courtesy Wikimedia Commons

This colorful and well-known silk moth is one of the largest in North America with a wingspan of up to 4.5 inches. They can be found as far west as the Great Plains, northward into Canada, and as far south as Northern Mexico.

Larvae or caterpillar

Photo courtesy my brother.

Adult moth

Photo courtesy Wikimedia Commons

This giant silk moth is found throughout the eastern half of the United States and lower parts of eastern Canada. The adult promethea exhibits sexual dimorphism with respect to coloration, meaning that males are distinguishable from females based on appearance. The above photo is a female. Males are a dark brown with similar wing markings. The average caterpillar length is 6.5-7cm.

Larvae or caterpillar

Photo courtesy Wikimedia Commons

Adult female moth

Photo courtesy Wikimedia Commons

The caterpillar of this species feeds almost exclusively on the tulip tree (Liriodendron tulipifera), which is where the name comes from. These moths are found from southern Ontario to central Illinois south to the Florida panhandle and Mississippi. Their wingspan can reach 80-110mm. The tuliptree silkmoth is very similar to the promethea, as can be observed in the photos.