Stonefly Identification Guide

Key Visual Features

Stoneflies are elongated, somewhat flattened insects tied to clean, flowing water. Identification points include:

• A body length that varies widely by species, from under half an inch to over 2 inches
• A flattened, elongated body shape, an adaptation for the nymphs to grip rocks in current
• Two pairs of membranous wings that fold flat and are held close over the back, extending past the tip of the abdomen — noticeably longer than the body itself
• Two long, thin tail filaments (cerci) projecting from the rear of the abdomen
• Long, thread-like antennae
• Coloring generally in muted browns, greys, yellows, or blacks, without bright patterning

Where and When You'd See It

Stoneflies require cold, clean, well-oxygenated streams and rivers for their aquatic nymph stage, so adults are found on streamside rocks, vegetation, and bridges near fast-flowing water. Many species emerge in early spring, including some cold-tolerant species active in late winter, while others emerge through summer and into fall depending on the species. Adults are typically weak fliers and are often seen crawling on rocks or low plants rather than flying long distances, staying close to the same stream that produced them.

Similar-Looking Bugs

• Caddisflies have hairy wings held in a steeper tent shape and long antennae, but lack the paired tail filaments seen on stoneflies.
• Mayflies also show two or three long tail filaments, but their wings stand upright and triangular above the body rather than folding flat, and their front wings are much larger than the hind wings.
• Dobsonflies and alderflies are generally larger and lack the long paired tail filaments, with more heavily veined, mottled wings.

Quick ID Checklist

• Flattened, elongated body shape
• Two long, thin tail filaments at the rear
• Wings folded flat and close over the back, extending beyond the abdomen tip
• Long thread-like antennae
• Found on rocks and vegetation beside cold, clean, fast-moving streams