09/06/2026
Our third water quality monitoring session of the year is now complete! As part of our ongoing monitoring program, we collected water samples from our six monitoring sites throughout the Meduxnekeag River and its tributaries. But we don’t just collect water—we also keep an eye out for the aquatic insects living in the river. These tiny creatures can tell us a great deal about the health of our waterways. Read on to learn more about one of the insects that we see quite regularly.
Meet the stonefly—one of nature's best indicators of clean, healthy water. Because stoneflies are highly sensitive to pollution, finding them in the Meduxnekeag River is a great sign that the river is supporting a thriving aquatic ecosystem. Read on to discover why these fascinating insects are so important.
Stoneflies are one of the three major groups that make up the EPT taxa, a collection of aquatic insects widely used by biologists to assess stream and river health. EPT stands for Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies). Because these insects are generally sensitive to pollution, their presence and diversity are strong indicators of good water quality.
During aquatic surveys, biologists compare the number and diversity of EPT taxa to more pollution-tolerant groups, such as Diptera (true flies, including midges). A higher proportion of EPT taxa generally indicates a healthier aquatic ecosystem.
Stoneflies are relatively large aquatic insects that spend most of their lives as nymphs, living underwater for one to four years, depending on the species. They have specific habitat requirements, including cool, well-oxygenated water, suitable streambed materials, and reliable food sources. Stonefly nymphs generally fall into two feeding groups: detritivores, which shred leaf litter or collect fine organic particles, and predators, which feed on other aquatic invertebrates.
Unlike mayflies and caddisflies, stoneflies emerge by crawling out of the water onto rocks, logs, or shoreline vegetation before shedding their nymphal exoskeleton and transforming into winged adults. While most species emerge from spring through fall, winter stoneflies emerge during late winter and early spring, making them one of the earliest aquatic insects to appear each year.
Adult stoneflies typically live for a few weeks and remain close to the stream, river, or lake where they developed. During courtship, males attract females by tapping or drumming their abdomen against a surface, creating species-specific vibrations. After mating, females return to the water to lay their eggs by dropping them onto the water's surface, dipping the tip of their abdomen into the water, or briefly submerging to attach the eggs directly to the streambed.
