Many species are voracious predators. While they are found in lakes, stoneflies prefer clean, cold flowing waters where there is a good supply of oxygen. The nymphs crawl clear of the stream before emerging as adults. Mayfly nymphs are very similar in shape to the stoneflies. These creatures dart, crawl, cling, and sprawl.
Mayflies inhabit all types of freshwater where the oxygen supply is good.
Most species prefer clean water. Mayflys and stoneflies have gills for oxygen exchange, however, a mayfly's gills are platelike and are located on its abdomen. These gills are moveable and they can flap them in still water to move more water across them. Like stoneflies, mayflies spend their early life stages in the water. They may be found in both streams or in ponds.