Many people wonder if large, winged insects like fish flies pose a threat. Adult fish flies do not bite humans. This article explains what fish flies are and why they are harmless, despite their sometimes intimidating appearance.
What Exactly is a Fish Fly?
Fish flies belong to the order Megaloptera, which also includes dobsonflies and alderflies. They are distinct from mayflies, though sometimes confused due to similar names and aquatic habitats. Adult fish flies typically measure 1 to 2.5 inches in length, possessing large, membranous wings that often fold flat over their bodies when at rest.
These insects are commonly found near freshwater sources such as rivers, streams, and ponds, as their larval stage is aquatic. The larval stage, often called a hellgrammite, lives underwater for an extended period, sometimes up to several years. After this aquatic phase, they emerge for a brief adult stage, which is primarily focused on reproduction.
The Truth About Their Mouthparts
Adult fish flies cannot bite or sting humans. Their adult mouthparts are underdeveloped, or vestigial, meaning they are not functional for feeding, piercing, or biting. This means they cannot inflict a bite, even if they appear large or somewhat menacing.
Unlike insects such as mosquitoes or horseflies, which possess specialized mouthparts for piercing skin and drawing blood, fish flies do not consume food during their adult lifespan. Their primary purpose in the adult stage, which typically lasts only a few days to a week, is solely reproduction. They rely on energy reserves accumulated during their longer larval stage to sustain them through this brief reproductive period.
Ecological Role and Human Interaction
Fish flies are harmless to humans, despite their size and occasional tendency to gather around artificial lights. While large swarms can be a temporary nuisance, they do not cause structural damage to homes or infest them. They are not venomous, and there are no known allergies associated with them.
These insects play a role in freshwater ecosystems. Fish fly larvae, the hellgrammites, are aquatic predators, feeding on smaller aquatic insects and contributing to the food chain. Adult fish flies serve as a food source for fish and other wildlife. Their presence often indicates good water quality, as their larvae require clean, oxygen-rich aquatic environments to thrive.