Culicidae family. These are the gnats and mosquitoes, there are 50 British species. Most adults are less than 6 mm long, and it is the females who suck blood to get the protein needed to produce eggs. There are about 3000 species world wide, many of medical and veterinary importance, e.g. some species transmit the pathogens which cause malaria (see Anopheles maculipennis below), yellow fever (see Aedes aegypti below right), filariasis and dengue. The adults have mouthparts adapted to both pierce and suck. The larvae and pupae are active swimmers. Right is the larva of the common gnat (Culex pipens). The eggs are laid on stagnant water surface (in the U. K. this is usually from April onwards) and the larva are aquatic. The larva feed on protozoans and other small organisms. They breathe through a tiny snorkel-like tube, so an oil film spread on water will cause them to die as the tube cannot break through the film. After pupating the males feed on nectar and plant

juices. Generally the males hatch a few minutes before the females, and dance in the air waiting for them to emerge. In most species the females need a blood meal in order to lay eggs. Individuals rarely fly more than a few hundred metres from their hatching site,

however mass invasions of towns can occur from as far as 100 kilometres. The common gnat usually gets her blood meal from birds, not man. Females of the common gnat hibernate as adults though the winter. They will have already mated and the males will all die once the weather gets cold.

When the female punctures skin she injects an anaesthetic which deadens the pain, and an anticoagulant to stop the blood clotting and to thin it making flow up her tubular tongue. She can drink up to three or four times her body weight in blood.

Adult males live for just over a week, but females can live as long as a month, and if it gets cold before she has laid her eggs she can hibernate. In temperate climates there can be 15 generations in the spring, summer, autumn period.

The way to tell a male (non-biting) from a female (biting) is to look at the antennae. The male has very bushy, plumose antennae, whilst the female has simple antennae. The antennae of the male is precisely tuned to pick up the exact frequency of the female's whining flight. This enables him to locate a suitable mate.

On the left is the pupa of a Culex sp. mosquito. It has breathing tubes, and at rest it lies suspended in the water with its breathing tubes just pushed slightly above the surface.

Mosquito flight speed has been recorded as 0.9 metres per second. Compare this with other insects.

On the right is an adult Anopheles maculipennis, a malarial mosquito. The abdomen has 8 segments.

The female lays her eggs on, or very near water in batches of 40 - 100. The larvae hatch in 2 or 3 days and feed on particles (mainly algae) in the water. When conditions are favourable the transition from larva to pupa can take as little as a week, during which the larva will moult 4 times. The pupal stage is more active and lasts for 2 or 3 days. When the adult is about to emerge the pupa straightens, sucks in air and floats to the surface. The skin splits longitudinally along the thorax, and the adult emerges.