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
