Aquatic larvae Left: mosquito Mosquito Ochlerotatus punctor Right: black fly larva and pupae.
Mosquitoes lay eggs in still water, such as ponds, ditch water and rain butts. They also use puddles, water-filled rot holes in trees and other small temporary water accumulations. These lack fish and other predators but may dry out before the larvae can complete their development. Mosquito eggs float on the water surface. When the larvae hatch, they swim in the water by flexing their bodies. They float up to the surface when they need to take in air. The pupal stage is shaped like a comma and is able to swim as actively as the larval stages. Mosquitoes can have several generations during the summer. Most species overwinter as eggs but some overwinter as adult females, which sometimes do so in buildings.
Black fly larvae require well oxygenated water, so they live in streams and rivers. The females deposit eggs on water plants or on wet mud of the river bank. The larvae attach themselves to submerged water plants, with their head ends extended into the water current. When fully grown they pupate in their larval feeding place. Adult flies emerge from the pupae underwater and float up to the surface. Black flies overwinter as eggs or larvae.
Biting midges and horse flies mostly lay their eggs in boggy ground and other places where the soil stays wet. However, larvae of Culicoides species of biting midge are semi-aquatic and develop in pond margins. Horse flies overwinter as larvae, with the pupal stage lasting for only a couple of weeks before the adult flies emerge in early to mid summer.
Role of biting flies in gardens
Biting flies can spoil the enjoyment of a garden. Mosquitoes, biting midges and black flies tend to be more active in the evening, while horse flies are active during the day. Covering up and insect repellent sprays and ointments may help keep these flies away (those containing Deet are probably the most effective) but retreating indoors may be necessary at times when biting flies are particularly active.
None of the biting flies currently found in Britain and Ireland transmit diseases such as malaria and yellow fever. However, due to climate change, it is possible that this situation will change. Ceratopogonid midges are responsible for transmitting some virus diseases of sheep and cattle, such as blue tongue disease and Schmallenberg virus, in the UK.
Other sources of information
Bass, J. (1998) Last instar larvae and pupae of the Simuliidae of Britain and Ireland. Freshwater Biological Association
Cranston, P. S., Ramsdale, C. D., Snow, K. R. & White, G. B. (1987) Adults, larvae and pupae of British mosquitoes (Culicidae). Freshwater Biological Association
Snow, K. R. (1990) Naturalists' Handbooks 24. Mosquitoes. Richmond Publishing
Stubbs, A. & Drake, M. (2014) British soldierflies and their allies. British Entomological and Natural History Society