CIRCULAR-SEAMED FLIES 3027 



but the choice of the female does not seem to be always restricted to matter of this 

 sort, since she sometimes selects meal, bread, or fruit, for the purpose. These flies 

 are liable to the attacks of a parasitic fungus {Empusa muscce) which causes their 

 death, and in autumn it is not uncommon to find their bodies killed by this means, 

 with the abdomen much distended, and showing the soft membrane between the 

 segments. The common bluebottle or blowfly {Calliphora erythrocephala) is too 

 well known to need description. One of the most noteworthy features connected 

 with this fly is the extraordinary keenness of the sense perhaps smell, which 

 enables it to discover the whereabouts of carcasses, however small, or of particles 

 of meat. In these it hastens to lay its eggs; and in a longer or shorter time, 

 according to temperature, the eggs hatch, and the larvae, feeding upon the meat, 

 rapidly grow until they reach maturity and pass into the pupa stage. Many persons 

 believe that bluebottles are full-grown examples of the house fly, and when in- 

 formed that such is not the case, and that these insects after reaching the winged 

 stage are incapable of growth, point out that bluebottles vary greatly in size, and 

 ask what may be the explanation of the difference. The answer is, that the size of 

 the bluebottle in its final stage depends upon the size of the maggot before 

 pupating, and the size of the maggot upon the amount of nourishment it is able to 

 obtain before its supply of food was exhausted. In any given case, when the sup- 

 ply is limited, the maggots that are the first to hatch will get more food than those 

 that appear later, and in consequence, when the whole of it is exhausted, will have 

 attained a greater length and fatness than the others, and thus become con- 

 verted into larger flies. Or, again, if three or four hundred eggs be laid in a 

 dead mouse and the same number in- a dead rabbit, it is clear that in the former 

 case the supply of food will be smaller for each larva, and will sooner come to an 

 end than in the latter. 



The gray flesh fly (Sarcophaga carnaria) is a handsome species, measuring in 

 the female half an inch in length. Seldom entering houses, it is not uncommon in 

 the open country, where it may be seen basking in the hot sun upon stones or 

 walls. Its prevailing color is pale slate gray, variegated on the thorax with black 

 bands, and the abdomen with square black spots, set corner to corner like the 

 squares of a chessboard. A noteworthy fact connected with this species is that the 

 eggs hatch within the parent before being laid, so that the young are born alive; 

 they feed upon decaying animal and vegetable matter. The blowflies belonging 

 to the genera Calliphora and Lucilia, respectively known as the bluebottle and 

 greenbottle flies, as a general rule deposit their eggs upon dead animal matter. 

 This, however, is by no means always the case, there being many instances on 

 record of the laying and hatching of the eggs upon living animals. Thus it is by 

 no means uncommon for sheep to be attacked in this way by a greenbottle fly (L. 

 silvarum}. On this subject, Mr. Reeks writes that "these flies deposit their eggs 

 in the wool of sheep, generally about the root of the tail or behind the shoulders, 

 anywhere, in fact, where the wool is most greasy. The larvae of these flies are 

 most troublesome to shepherds in the latter part of May and June, until the sheep 

 are sheared, and much later in the summer with lambs, when they should be dipped 

 in a preparation of arsenic and soft soap. ' ' Toads and frogs also seem to be fre- 



