Stoneflies do most of their eating while they are in the larval stage, during which time they capture and eat other small insects and invertebrates. The adult stage of a stonefly's life cycle is primarily concentrated on breeding, and many species die shortly after breeding. While some adult stoneflies do not eat at all, others consume pollen or algae.
There are 3,000 species of stoneflies worldwide, and different breeds have slightly different habitats and preferences. Most stonefly species are very inconspicuous insects. They spend most of the day hiding amongst vegetation. At night, they take flight and look for mates. When depositing their eggs, the females place them in water. Most stoneflies inhabit the rapidly flowing portions of rivers and streams. Such places have higher levels of dissolved oxygen, which the stonefly larvae require for growth. Usually, the larvae will crawl under rocks for protection from predators and the swift current. The larvae of some stonefly species take an extended period of time to develop into adults. Some species remain underwater for two years or more.
Because stoneflies require cool, clean, highly oxygenated water, they are often used as an indicator species that signifies the water is very clean. Stoneflies, particularly the larvae, are an important food source for river fish, such as trout, bass and sunfish.