Fly (Shore fly) Family: Ephydridae
Common names: Shore fly, Brine fly
Flies in the Ephydridae family are tiny flies that can be found near seashores or at smaller inland waters, such as ponds. About 2,000 species have been described worldwide. In New Zealand they are among the less common true flies in our fresh waters. Ephydridae are minute to small (0.9 to 7.0 mm.) flies, black or grey. Wings are sometimes patterned. The ratio of the vertical diameter of eye and the height of gena (face index) is widely used in identification of this species.
Ephydridae live most of their lives underwater. Their life cycle begins in the summer, when the female flies lay their eggs on the water surface. The hatched larvae have a maggot-like body with a velvety surface texture, and at the end of the abdomen there are two respiratory siphons or (rarely) two black hooks. There is no visible head. Some species have caterpillar-like pseudopods along the underside of the body.
They are found in many stream types including algae-covered streambeds, and some species are common in geothermally heated waters. The larvae graze mostly cyanobacteria (get energy through photosynthesis), other types of bacteria, bottom-dwelling algae, diatoms, and detritus on submerged surfaces. They prefer to live in muddy areas rather than in sandy areas. In autumn the larvae become inactive and remain that way until temperatures rise in the spring when they start feeding. In late spring or early summer, they begin metamorphosis. They attach to solid objects under the water then grow hard brown pupal case around their bodies. Inside, the flies begin transforming into adults. Depending on the water temperature after a few weeks the adults emerge and float to the surface. The adults can walk on the surface of the water feeding on algae and bacteria growing in the surface film. They only live as adults for a short period during which they mate and lay eggs.