The caddisflies are an order, Trichoptera, of insects with approximately 7,000 described species. Also called sedge-flies or rail-flies, they are small moth-like insects having two pairs of hairy membranous wings. They are closely related to Lepidoptera (moths and butterflies) which have scales on their wings, and the two orders together form the superorder Amphiesmenoptera. Caddisflies have aquatic larvae and are found in a wide variety of habitats such as streams, rivers, lakes, ponds, spring seeps, and temporary waters (vernal pools). The larvae of many species use silk to make protective cases of gravel, sand, twigs or other debris. The name "Trichoptera" comes from Greek: θρίξ (thrix, "hair") + πτερόν (pteron, "wing").