Pest Identification

Learn More About the Pests Invading Your Home

Pest Identification: Alderflies

Most Common Types

There are about 65 species of alderfly, part of the order Megaloptera which includes the closely related dobsonfly and fishfly.


What They Look Like

Adult alderflies are dark brown or black, about 1 inch long, and have long delicate antennae. They are distinguished by two pairs of lacy brown or grey wings which are folded in a tent-like manner. With a wingspan of 0.8 to 1.3 inches (22mm to 34mm) the wings are longer than the body.


Where They Live

Alderfly larva are aquatic carnivores that live in the silt at the bottom of ponds and slow-moving streams and rivers. They remain active in water for one to two years before crawling onto land and entering a pupal stage. After alderflies metamorphose into adult insects they remain near the waterway where they hatched.


Where They Nest

Alderflies emerge in large numbers in late spring and early summer and live a few days— only long enough to mate. Female alderflies lay large numbers of eggs on grass stems near streams and rivers. When the eggs hatch, the larvae crawl or drop into the water.


Steps to Prevent

Alderflies are part of the natural ecology of springs, rivers, reservoirs, and other bodies of water and do not need to be controlled.


Are They Harmful?

Alderflies are not harmful to humans and are valued by fly fishermen who use them as bait.