A few species of moths ingest plants that contain cardenolides, a group of poisons that affect the heart muscle and are dangerous to humans when eaten. Otherwise moths are harmless. Moths do not bite or sting, and they have many beneficial effects on the ecosystem.
Larvae and adult moths provide food for predators such as birds, bats, frogs and spiders. Most moth species feed on nectar and spread pollen among flowers. Other adult species do not feed at all. Moths in the larva stage that gather in large numbers may damage crops. Additionally, the gypsy moth destroys trees. Of the 15,000 moth species in the United States, only two damage items made from wool, silk, fur and feathers.