Non-biting midge

Summer visitors to the more attractive parts of Scotland will not need reminding that such places are often infested with a particularly vicious form of biting midge that can make life extremely uncomfortable unless anti-midge precautions are taken. However, there is another species of midge that should cause outdoor adventurers no problems whatsoever.

The non-biting midge (Chironomus plumosus) has very weak mouthparts and most of them are unable to feed, hence they have no cause to bite humans or livestock. The function of the adults is only to mate, following which they die soon afterwards.

A common sight near watercourses on warm summer evenings is a cloud comprising hundreds of thousands of midges preforming mating dances. After mating has taken place the females will lay their eggs on the surface of the water, vast numbers of which then form a spiral jelly-like rope that attaches to an underwater plant or other object.

On hatching, the larvae are extremely vulnerable as a food source for other water dwellers such as small fish, but the survivors will go through a number of moults as they feed and grow.

Between April and September, in slow-moving streams and especially ones that are polluted with sewage, large numbers of bright red midge larvae known as bloodworms can be seen. These are stiff, segmented worms that grow up to 0.75 inches (20 mm) long. They have stumpy projections at each end that are called prolegs.

After the final moult the larvae turns into pupae that are able to swim and breathe by means of gill filaments on the thorax. The pupae, which are 0.4 inches (10 mm) long, split open to release the adult midges.

Adult non-biting midges are about 0.25 inches (6 mm) long. Male midges have feathery antennae, but the feathers are missing from the antennae of female midges. There is a pronounced hump on the thorax.

© John Welford