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it need only be a trickle. Having said that,
it should be noted that adults can be found up
to two miles from their breeding grounds.
They are also very intolerant of polluted
waters and consequently their numbers in the
London area have declined drastically over the
last century or so.
The adults are larger than the midges but
smaller than the mosquitoes. Being about 4 mm
long and rather squat in appearance, the wings
are clear as opposed to the grey marked wings
of the midges.
Overseas there are records of farm animals
being killed by repeated attacks of Simuliids
and the insects are known to transmit various
human diseases. Their greatest public health
importance lies in their role as vectors of the
filarial nematode which causes river blindness,
of which it is believed that between twenty and
thirty million people are afflicted worldwide.
They also transmit other nematodes and several
types of blood parasite to man as well as other
animals. In Britain they have been implicated
in transmitting nematodes to horses. But as
far as man is concerned, the worst we will
suffer is one or more painful lumps.
There only remain the three species of the
family Muscidae that suck blood, though only
two of these bite man. I suppose one could
argue that these flies are twice as bad as the
other bloodsuckers, in that both the males and
females take blood. These flies look very
much like the ordinary house fly, belonging to
the same family. However, on closer inspec-
tion, even with the naked eye, one can always