Adult io moths do not have any urticating scales. They range west to southern Arizona and south to Central America, at least as far as Costa Rica. Adult males are mostly yellow, while females have brown forewings. The larvae have characteristic long yellow or green spines covering most of the body. Only a few other caterpillars may look similar, but these do not have the well-defined red and white lateral line.
Earlier instars are yellow overall and the lateral line is reduced.
After several weeks of feeding, they make a simple paper-like cocoon away from the host plant. In Florida, there are three to four generations per year. There usually is only one generation in northern states. The io moth has a long list of host plants, with over 100 recorded plant genera in North America, including such diverse plants as roses, cotton, hibiscus, azaleas, willows, clover, and palms. In Florida, io moth larvae are commonly found on oaks and other hardwoods.