Large swarms of mating mayflies and caddisflies often occur when all the individuals of a single species emerge at the same time. Stoneflies crawl out of the water and mate on the ground. The females of all three groups fly upstream and drop their eggs onto the water or dive into the stream to attach them to rocks or leaves. After emergence, adults fly for a short time but return to the water to feed in the same habitat as the larvae. Both the larvae and adults are rather small, dark-colored, and tend to drift to the bottom of a sample so they may be hard to see.
Riffle beetles collect and gather a variety of different foods.
There are many species of true flies, but you are likely to recognize three main groups or families. They are often attached to debris by their tiny legs. They attach themselves to the substrate and prefer soft sediment. Nematodes and oligochaetes are long and thin and writhe like snakes. Note that these animals do not have legs.