736 The Living Animals of the World 



V 



animals ; or, when that fails them, they may 

 attack caterpillars, or other small soft-bodied 

 creatures. Though not very particular about 

 their food, different species are more or less 

 attached to different animals; and while in 

 Europe the most troublesome species is the one 

 considered to be most particularly attached to 

 man, the species most troublesome in North 

 America is known in Europe as the DOG-FLEA. 

 They are all very similar in habits and appear- 

 ance. Fleas are not only annoying, but, in con- 

 junction with rats, are believed to be among the 



photo by w. P. ixtndo, F.z.s.i ' (Cent's ra,k. principal agents in the spread of the plague. There 



BEE-FLY. i g another insect called the JIGGER, or SAND-FLEA, 



similar to the fly which destroys the locust eggs in Cyprus. common in most of the warmer parts of America, 



and which has more recently been introduced 



into Africa. The female burrows into the feet of men or animals, where her body swells up 

 with eggs to the size of a pea; and serious and sometimes fatal ulcers are the ordinary result, 

 unless the insect is carefully extracted at an early stage of the attack. 



USES OF FLIES. 



It must not be supposed from the foregoing observations that flies are simply and solely 

 pests to man and beast, without any redeeming qualities. Their services are less required in 

 cold and settled countries, but in warm climates their value as scavengers can hardly be 

 over-estimated. As regards the removal of carrion alone, Linnaeus declared that the progeny 

 of only three blow-flies would devour the carcase of a dead horse as quickly as a lion a 

 statement which, even if slightly exaggerated, conveys a vivid idea of their voracity and the 

 rate at which they increase. 



Flies are also useful in keeping down the multitudes of destructive insects. Numbers of 

 caterpillars fall victims to the bristly flies alluded to on the last page ; and the Bee-flies, which 

 form a family placed next to the Gad-flies, render far greater service in destroying locusts. 

 They much resemble small humble-bees, being very much the same shape, and they are 

 clothed with yellow down in the British species, and the transparent wings are conspicuously 

 marked with black bands (as in the photograph above), or with brown shading and spots. 

 The insects have a very rapid flight, and use their long proboscis to suck the honey of 

 flowers ; but their grubs are parasitic at least in some instances on wild bees ; and it is 

 probable that their resemblance to bees has some reference to this mode of life. But in 

 Cyprus, Algeria, North America, etc., the larvse of allied species feed inside the egg-cases 

 of locusts, sometimes destroying as large a proportion as four-fifths of the whole brood. 

 Locusts have many enemies, but it will easily be seen that the attacks of foes like these 

 must reduce their numbers considerably, notwithstanding the swarms which frequently survive, 

 and which are liable to the attacks of other enemies, such as robber-flies, locust-birds, etc., 

 after they have actually arrived at maturity. 



Nor must we omit to notice the use of flies as articles of food for man or useful 

 animals. Many persons are very fond of cheese-hoppers, which are really the maggots of a 

 small fly ; and we read in Kirby's " Textbook of Entomology," page 92 : " The Rev. A. E. 

 Eaton informs me that he believes that two species of Ephemeridce (May-flies) form a portion 

 of the so-called ' Kungu Cake,' manufactured by the natives of South Africa of gnats, arid 

 probably any other insects which can be obtained in sufficient abundance." "Gentles," which 

 are the maggots of flies, are used by anglers for ground-bait. 



