336 THE LIVING ANIMALS OF THE WORLD 
The ROBBER-FLIES are large flies, with long, tapering bodies, of a black or partly yellow 
colour, and feed on smaller flies and other insects of different kinds. They have very thick, 
hairy legs, and a strong proboscis. A handsome Australian species, allied to these, but with a 
broader body, is represented in the Coloured Plate. . 
The HORNET ROBBER-FLY, represented on page 731, is one of the most conspicuous of 
the British species. Among other places, it may be seen flying over the short grass at the 
top of the cliffs between Brighton and Rottingdean. They are very predaceous, and are 
probably rather beneficial than otherwise, by contributing to keep down injurious insects. 
But in North America there is a species called the BEE-KILLER, which is an extremely 
destructive insect, taking up its station in front of a hive, and killing large numbers of bees 
as they fly backwards and forwards from the hive. 
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 
“ ee of horses, or in the nostrils and other cavities in the heads of 
| sheep or deer. 
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 
Ehate Oy ME Be Dang EO zeNs puncture like a gad-fly. This is the meaning of the popular 
se ge ea O8 saying that “ the flies bite in rainy weather.” 
Tite parecraph Ae ais Sandee 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 ¢horough 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 
