Aquatic Insects At work:
We depend on clean water for drinking, bathing, and recreation. Biologists look to aquatic insects for help in monitoring the water quality of streams, rivers, and lakes. Chief among these insects are mayflies, stoneflies, and caddisflies, the “EPT Index” for water quality. The adult insects live on land and often fly to outdoor lights at night.
Ephemeroptera – Mayflies
The “E” in EPT are the mayflies. The adults live only a day or two, just long enough to mate and reproduce; but the larvae, also known as nymphs or naiads (NYE-adds), live underwater, breathing through gills. Most live three to six months, but the egg stage beforehand can last nine to eleven months in some species. Many species sprawl on the bottom of streams, rivers, or lakes, while others cling to or climb aquatic vegetation. Some are burrowers in the bottom sediment. Most feed on organic detritus they “gather” or “collect,” but others are “scrapers” that graze on algae. Still others are “shredders” of decaying leaves and such, and a few are predators on other aquatic organisms.
Plecoptera – Stoneflies
The “P” in EPT are stoneflies. Larger species may take 2-3 years to complete their development from egg to naiad to adult, but most take only one year at maximum. The aquatic naiads behave similarly to mayflies in lifestyle, varying from species to species. Several kinds are underwater predators.
Trichoptera – Caddisflies
The “T” in EPT are caddisflies. They are share similarities to moths and butterflies, with worm-like larvae that live underwater. Larvae may spin nets or “bags” to catch prey or filter microorganisms from swift currents; or they may build “mobile homes” of plant debris or pebbles or sand to disguise and protect them from predators. A few burrow into the sediment at the bottom of watercourses or lakes. Most of these case-makers are shredders, collectors, or scrapers of decaying plant matter, but some feed on living aquatic plants. The adult insects are moth-like and are easily mistaken for moths. They may fly some distance from water in the course of finding mates.
Sensitivity and Fly Fishing
A good number of different families within these three orders of insects are highly sensitive to chemicals and other pollutants in freshwater ecosystems. Their presence in a stream, river, or lake is thus a good indicator of water purity. Their absence may be of concern if they are present in other waters in a given geographic location. Furthermore, anglers rely on the regular, dependable “hatches” of many of these species to model artificial flies for fly fishing. This is a huge recreational industry that can only thrive on clean, clear water.