336 THE LIVING ANIxMALS 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 difterent 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. The)- have the habit of hovering motionless in the 



air, and then darting oft" suddenly. Some of the larger species proceed from curious maggots, 



with long tails, which have been compared to the tail of a rat. These li\e 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 



livin" 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. 



The House-flies and their allies form a very large group, 



di\-idcd into many families. The true house-fly is an autumn 



insect; but there are other flies which resemble it which live 



in houses at difterent times of the year. Most of them are 



harmless, although there is one species, very like a house-fly, 



[- which comes into houses in rain\' weather, and inflicts a 



FhM bv ir. F. DaTidt, F.z.s. puncture like a gad-fl}'. This is the meaning of the popular 



BLUE-BOTTLE FLY, OR saying that " the flies bite in rainv weather." 



BLOW-FLY 



, . . . Although house-flies do not bite, \-et they are sometimes 



lAis photograph ihoii's the tvtngs expanJeJ ^ ^ ' ' 



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 \-ery 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-li\ed predecessors) was a paper read by 

 William Spence at the meeting on April 7, 1834, about a year after the Society had been 

 definitely foimded, 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 \-ears, 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-DAV Fi.v, and is often seen in considerable 

 numbers, in the hottest part of the day, fl>'ing 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 



