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Marine Animal Encyclopedia

Kelp Fly Coelopa frigida

The most widely distributed of the seaweed flies, the kelp fly is found almost everywhere there is rotting seaweed along a strand line. They have flattened, lustrous black bodies, tinged with gray, and bristly, brownish yellow legs. Of the two pairs of wings, only the front pair is functional, the hind pair being modified to small club-shaped halteres that act as stabilizers when in flight. Kelp flies can crawl through vast layers of slimy seaweed without getting stuck, and if immersed in seawater they simply float up to the surface and fly off. Their larvae are equally waterproof. Strongly attracted to rotting seaweed by its smell, the female kelp flies seek out warm spots in which to lay their eggs. The larvae hatch and feed on the seaweed around them. After three molts they pupate; the adults emerge and complete the life cycle about 11 days after the eggs were laid. Kelp flies are an important food source for several coastal birds, including kelp gulls and sandpipers.

Kelp Flyzoom image
  • Subphylum Insecta
  • Length – in (3–10 mm)
  • Habitat Temperate shores with rotting seaweed
  • Distribution North Atlantic and north Pacific shorelines
Kelp Fly habitat mapzoom image