294 Marvels of Insect Life. 



that we had only got rid of the attentions of one class of pests to fall under the care 

 of another group. Even Mrs. Troglodyte-Smith must have found that there were 

 undesirable creatures who insisted upon sharing her cave. Another fact that 

 militates against the success of the fly leagues is the war that has been waged in 

 late years against the wasp, one of the most inveterate destroyers of flies. 



Some of these sanitary or scavenger flies, though their habits in the larval 

 stage are similar to those of the blow-ff}', rarely or never enter our houses, and there- 

 fore do not become a nuisance to us. Such are the green-bottle ^ and the flesh-fly.'^ 

 The first does occasionally wander into open windows and doors in the summer, 

 bp.t does not stay in the house, preferring to sit on leaves in the hottest sunshine 

 and exhibit its shining golden-green livery to the best advantage. The green- 

 bottle is the special bane of the fishmonger, and if by chance we pass by the back 

 premises where this tradesman temporarily stores his refuse, w^e shall startle up 

 a cloud of these beautiful but repulsive Insects, who have been engaged not only 

 in depositing eggs in the offal, but in sucking up the more fluid decomposing portions. 

 The flesh-fly is similar to the blow-fly, but rather longer and of a grey and black 

 coloration instead of the steely-blue which has given the name of blue-bottle. It 



is a carrion-feeder, but out of doors ; 

 and it retains its eggs until they are 

 hatched, so that on the discovery of 

 suitable material for their deposit the 

 sanitary work of clearing away dan- 

 gerous matter begins at once. In 

 this connection it is worthy of note 

 that these flies have had all the details 

 Photo by] iH.s.a,eavtn.F.R.M.s. ^^ ^hcir lifc-history adapted to the 



Balancer or Hind-Wing of House-Fly. necessities of the case. A heap 



Tlie balancers or halteres are like minute wings, and probably represent of stable mailUrC IS IcSS mimical 

 the hinder wings of the four-winged orders. They are believed to be 



sense organs. to animal lifc thaii is decomposing 



flesh, and as innumerable beetles and flies help to clear it away, the fecundity 

 of the house-fly is not nearly so high as that of the blue-bottle and flesh-fly, 

 whose work must be done much more expeditiouslv. We have mentioned 

 that the house-fly lays about six hundred eggs ; the blow-fly lays from five 

 hundred to a thousand, but dissection has shown that the flesh-fly is able to 

 deposit as many as twenty thousand. Of course, these are not all deposited at once, 

 or in the same mass of corruption : thev are laid in batches as appears to be necessary. 

 But it frequently happens that a number of egg-laden blow-flies or flesh-flies will 

 lay their eggs in the same food-mass, which may not be sufficient to bring so vast 

 an army of maggots to their full size, in that case some would feed upon their 

 weaker kindred, so that a few could come to maturil\' and continue the race. The 

 dead matter would be converted rapidly into living matter, and so cease to pollute 

 the atmosphere. The futility of attemj^ting to get rid of the fly-nuisance by killing 

 a few thousand flies here and there is api)arent. It is akin to emptying the ocean 

 with a tea-spoon. 



We have spoken of all these flies as laving eggs, but it should be ivmembered 



' I.ucilia cLcsar. - Sarcophaga carnaria. 



