Io Moth (Automeris io)

The Io moth, also known as the "Peacock moth," is one of the smaller North American silk moths with a wingspan of 2-3 inches. The female is noticeably larger than the male and its forewing is a purple-brown color. The male's forewings are mostly yellow. Both sexes have a beautifully colored underwing marked by a black dot. Hence the peacock nickname and the "bullseye" nickname of some of its close relatives, particularly the Mexican Bullseye moth.

As with all Saturniidae moths, the Io does all its eating in the larva stage. The adult moth has no mouth and cannot eat. It ranges throughout the eastern half of the United States to Iowa and Missouri, sometimes extending into the central states.

The larva is green with red stripes and is covered with spikes that are quite irritating to the skin when touched, and very painful if one of the spikes gets stuck in your skin. Younger caterpillars are softer and are less likely to cause irritation. The first instars are very gregarious feeders. They are often found on the undersides of leaves. Their host plant is almost any tree or large bush. We have fed them apple and maple with success. They will also eat rose, cherry, and others.

Click on any of the thumbnails to get a larger picture.

Female

Male

Caterpillars

(622 Kb)	Here's a picture of some newly hatched io larva and eggs (Caution! The picture is a high quality image - 622 Kb, but well worth the wait!). They're about the width of a pin head and not much longer. The larva are brown with soft bristles. Note the eggs on the right side with black dots on one end. The dots signal that the eggs are fertile. On the left side you can see an egg with a longer brown area (look toward the end of the branch). This is an io larva that's about to hatch.
	To the left are first instar Io. They are mostly brown with lots of soft bristles. In these early instars, the caterpillars are very gregarious, always feeding in groups.
	This is the second instar Io. They are mostly yellow with soft bristles. Their red and white stripes are beginning to appear on their sides. Note that they still tend to feed in groups.
	This is the fifth instar Io. It is about 2.5 inches long, mostly green in color with maroon and with stripes down its side. On our apple tree, it's amazing how much the stripes look like branches, making the caterpillar difficult to find on the first pass. There are also rows of green spikes along the body. You don't mess with these caterpillars. The spikes are painful to the touch. Just brushing against them gives a sensation very similar to Nettles plants that lasts a half hour or so. I've never actually grabbed a fifth instar, and am not inclined to do so. When I need to move these, I use heavy gloves and a light touch. My four-year old once "petted" one before I could tell her it would hurt. She shrieked for nearly 10 minutes! And complained for another hour!
	Here are a number of 5th instars. You can see the spikes more clearly in these picture. The red and white stripes add interesting coloration to the caterpillar.