This fly lays its eggs in manure or other refuse, these hatching out, passing through all their stages and emerging as perfect insects in a few days. Their uncleanly habits make the house flies most efficient agents in the carriage of different diseases, especially typhoid fever and others which attack the digestive tract. Flies are therefore not merely a nuisance to be deplored, but a positive danger to mankind. Among other flies are the carrion flies, black flies, the gnats and the mosquitoes, all troublesome to man, while others attack various plants.
THE LARGE VORACIOUS
FLEAS
Of these the breeze-flies or gad-flies possess powerful piercing mouth-parts, with which they torment both stock and human beings. A well-known species is the long brown clegg (Hæmatopota pluvialis), often met with in woods. In some tropical kinds the jaws are of enormous length.
Robber-flies are voracious and insatiable forms which prey upon other insects, even wasps and tiger-beetles being among their victims.
Hover-flies are swift and elegant insects which have already been mentioned in connection with flowers. Some of them closely resemble bees in appearance.
The dreaded tsetse fly (Glossina morsitans), so fatal to horses in parts of South Africa, belongs here. Germs of the fly-sickness (Nagana) are introduced into the blood of the victims, Tsetse flies of other species are responsible for “sleeping sickness,” which makes parts of tropical Africa uninhabitable.
THE PESTIFEROUS MOSQUITOS
AND GNATS
These are particularly notable for the blood-sucking propensities of the female. Some tropical mosquitoes disseminate the germs of such diseases as malarial fever. Wholesale destruction of the early stages, by pouring petroleum on the surface of the stagnant water in which they live, has been employed with conspicuous success at Havana and in the Panama Canal zone as a preventive measure against yellow fever and malaria.
Midges are very minute gnats, of which the aquatic larvæ are known as blood-worms.
THE WINGLESS FLEAS
AND OTHER PESTS