Emperor moths

Overview

Saturniinae is a subfamily of emperor and giant silk moths (family Saturniidae). They are commonly known as emperor moths or wild silk moths. There are currently 1,391 recognized Saturniinae species in 76 genera, most of them in 2 tribes, worldwide, 17 to 21 species in 8 to 10 genera in 2 tribes in North America north of Mexico, and at least 5 species in 4 genera in 2 tribes in Minnesota.

Emperor moth adults do not feed and they are short lived. They are mostly active at night, often not until a few hours after sunset, and they are attracted to lights. Some rest with their wings spread flat. Many rest with their wings tightly closed over their abdomen. When disturbed, they drop to the ground, mimicking a falling leaf.

Mature caterpillars overwinter as pupae in a strong, silken cocoon, emerging as adults the following spring.

All attempts to create a silk industry using North American silk moths have failed. The primary source of silk for textiles is domesticated silkmoth (Bombyx mori), as it has been for more than 4,000 years.

Description

Emperor moths are striking, large to very large moths. Their large size may have evolved as a defense against small bats and birds.

On males, the antennae are feathery with two branches on both sides of each segment (quadripectinate). The branches (rami) are long, slender, and straight or only slightly curved. They are well separated at the base, and they continue nearly to the end of the antenna. On the female, the antennae are also quadripectinate except in the genus Saturnia, which does not occur in Minnesota. The rami are much shorter than those on the male.

The wings are broad, membranous, and flat, with very little structural relief or curling. They are essentially flat sheets attached to the body, which contribute to their large surface area and often striking appearance. They have colorful patterns that often include eyespots. There is always a color patch near the tip (apex) of the forewing. It may be a patch nearly at the tip, as in the polyphemus moth, a streak, as in the luna moth, or an eyespot, as in the cecropia moth.

On the legs, the spurs on the fourth segment (tibia) are short and are concealed by hairs on the leg.

The caterpillars are large, robust, and greenish. In some species, hairs (setae) or short spines rise from the tips of pairs of brightly colored raised projections (tubercles). The tubercles may be elongated, knob-like, or almost flat, plate-like. On the eighth abdominal segment the tubercles are united into a single middorsal tubercle. The setae and spines do not sting.