200 OUR HOUSEHOLD INSECTS 



which they find themselves, and hence, unlike the perfect 

 insects, are furnished with a biting apparatus, which is 

 in the form of two strong hooks. These are cast off 

 when the pupa stage is reached, and left behind with the 

 pupa case on the emergence of the perfect fly. The 

 trifling amount of locomotion necessary to the maggot 

 is performed by muscular contortions of the body, aided 

 by the hook-like jaws, and by rows of tiny hooks at the 

 junctions of the segments. The larval life, as we have 

 already said, is but short; that of the house fly, for 

 example, lasts about a week, during which time the 

 maggot is said to change its skin twice, altering its form 

 to some extent on each occasion. By the end of this 

 time it is full-grown, and passes into the pupa condition, 

 which in about another week gives place to the perfect 

 form. The larvae are apparently tenacious of life, and 

 can continue to exist even under very unfavourable con- 

 ditions. Thus it is recorded in the French Naturalists 

 of the maggots of a bluebottle, that they had been put 

 into an aquarium to serve as food for the newts, and two 

 days afterwards they were still alive, and some had even 

 changed into pupae, though at the bottom of the water. 

 They are very dependent on temperature, and unless 

 there is sufficient warmth their development is delayed, 

 and they become more or less dormant ; hence all speci- 

 mens that are in the larval or pupal condition at the 

 approach of winter have their further development 

 stopped, and remain in a torpid condition till the return- 

 ing warmth of spring enables them to complete their 

 cycle of changes. 



The pupae are extremely peculiar. With most in- 

 sects, it is customary for the pupal condition to be 

 assumed by means of a casting of the last larval skin. 

 Such, however, is not the case with these flies; but 



