Simulidae family.

These are commonly known as the black flies. The adults (see left) are small, grey and have broad wings. The female bites man, and in the U. K. the adults fly from March to November. She lays her eggs in a jelly mass or in strings on stones and weeds near the water's edge. The larva (see below) enters the water when it hatches out of the egg and attaches itself to the underside of a stone, or a plant leaf or stem. The larva is cream or grey in colour and eats plant particles. The larva has a "leg" on its thorax which ends in a sucker for holding on to surface against a current of water. It has anal gills and an attachment organ of strong hooks on its last abdominal segment. It uses the attachment organ and sucker to creep along surfaces. Like a spider it can let out a "life line" when strong currents detach it, and haul itself back to its original position. In some species a fully grown larva can be as long as 2 cm. Before pupating it constructs a cocoon and attaches it firmly to a solid object.

Chironomidae family (below)

There are over 380 British species, most of which are difficult to identify to species level. The adults are like gnats, and the males have hairy antennae. The males swarm around dusk, and dance for the females who sit safely on the ground or on vegetation. When a female has made her choice of male she flies up to him and they mate on the wing. They can be seen throughout the year in the U. K. Few species have jaws strong enough to pierce human skin. Most species have aquatic larva, but other larva live in moss, dung, rotting wood or decomposing vegatation.