Adult stoneflies have long antennae, weak, chewing mouthparts, and two pairs of membranous wings. The hindwings are generally larger and shorter than the forewings and fold like a fan when not in use. They range in size from 6 to more than 60 mm (0.25 to 2.5 inches).


The nymph feeds on plants, decaying organic matter, and other insects. Adult stoneflies can be herbivory (mostly shredding, but also scraping, gouging, and general gathering) or predators that eat other bugs.


Stoneflies are subject to predation from larger invertebrate predators (e.g., hellgrammites) and fish.

Reproduction and Life Cycle

Mayflies remain in the nymphal form for one to four years, depending on species, and undergo from 12 to 36 molts before emerging and becoming terrestrial as adults. Before becoming adults, nymphs will leave the water, attach to a fixed surface and molt one last time.

The adults generally only survive for a few weeks, and emerge only during specific times of the year when resources are optimal. The female can lay up to one thousand eggs.

Did You Know?

  • Stoneflies, along with mayflies and caddisflies, are important biotic indicators of water quality.

Sources and Additional Information