The Hover-flies are brightly coloured, rather smooth flies, and are familiar objects in gardens, and in open places in woods. They have the habit of hovering motionless in the air, and then darting off suddenly. Some of the larger species proceed from curious maggots, with long tails, which have been compared to the tail of a rat. These live in putrid water; and as the flies have a slight resemblance to bees, the fact is believed to have given rise to the old fable that bees are generated from the rotting carcases of oxen or other large animals.
The Bot-flies are remarkable for being parasitic on warm-blooded animals, their maggots living in tumours on the skin of oxen, known as "warbles," or in the stomach and intestines of horses, or in the nostrils and other cavities in the heads of sheep or deer.
Photo by W. P, Dando, F.Z.S., Regent's Park.
BLUE-BOTTLE FLY, OR BLOW-FLY.
This photograph shows the wings expanded.
The House-flies and their allies form a very large group, divided into many families. The true house-fly is an autumn insect; but there are other flies which resemble it which live in houses at different times of the year. Most of them are harmless, although there is one species, very like a house-fly, which comes into houses in rainy weather, and inflicts a puncture like a gad-fly. This is the meaning of the popular saying that "the flies bite in rainy weather."
Although house-flies do not bite, yet they are sometimes exceedingly troublesome when they are in unusual numbers; and as they settle everywhere, they may convey infection mechanically, though not as the principal agents in the dissemination of definite diseases, like the mosquitoes. Thus, in Egypt, they are said frequently to convey ophthalmia, a very prevalent disease in that country.
The very first paper published in the "Transactions of the present Entomological Society of London" (for the existing Society had several short-lived predecessors) was a paper read by William Spence at the meeting on April 7, 1834, about a year after the Society had been definitely founded, entitled "Observations on a Mode practised in Italy of excluding the Common House-fly from Apartments." This desirable result is attained simply by stretching a net of white or coloured thread, with meshes of an inch or more in diameter, across an open window, which the flies will not venture to pass, if the room is lighted from one side only—"for if there be a thorough light either from an opposite or side window, the flies pass through the net without scruple." Mr. Spence's son also referred to a passage in Herodotus where he says that Egyptian fishermen in his time defended themselves from the gnats by covering their beds with the nets which they had used in the day for fishing, and through which these insects, though they bit through linen or woollen, did not even attempt to bite. The matter seems to have been overlooked in recent years, though it is evidently well worthy of consideration when flies or gnats are troublesome.
There is a conspicuous insect allied to the house-flies, but a little larger, measuring about half an inch in length. It is called the Noon-day Fly, and is often seen in considerable numbers, in the hottest part of the day, flying round and settling on the trunks and leaves of trees; it also settles on cow-dung. It is a shining black fly, with the sides and under surface of the head golden yellow in the male; the wings are transparent, slightly tinged with pale brown, and bright rusty yellow towards the base.