Drosophila or Caddisfly?
Contrary to popular belief, caddisflies do not belong to the order Diptera, so they are not flies. They are part of the order Trichoptera. While the Diptera group, including the fruit flies (Drosophila spp.), contains over 18,000 species in the United States and Canada, there are approximately 1,200 types of caddisflies in North America alone.
Flies from the Diptera order have only one pair of wings, while caddisflies have two pair of wings. Many flies lay their eggs in decaying or fermenting material. When fly eggs hatch, the larvae eat the decaying material where they hatch. However, caddisfly larvae feed on detritus material from the bottom of lakes or rivers. This is because caddisflies lay their eggs on the surface of bodies of water.
The habitats and breeding grounds of flies and caddisflies are also very different. While flies can be found most everywhere, including tropical regions, deserts and swamps, caddisflies are found near lakes and streams. Caddisfly larvae remain in the water until they have developed fully into adults. During their development, caddisfly larvae construct protective casings from twigs, sand, silk and other found objects. Dipteran larvae are often terrestrial and usually do not build cases until they begin the pupal stage of their life cycle.