180 



MORE MINOR HORRORS 



grown it attains a length of 11 mm., and the 

 larval stage usually lasts from two to three 

 weeks ; but development may be retarded 

 by adverse circumstances up 

 to eleven or twelve weeks, 

 and in such cases the full- 

 grown larvae are often 

 stunted in size. In these cir- 

 cumstances the pupae they 

 produce are markedly smaller 

 than those which have fol- 

 lowed a more normal course 

 of development. As is true 

 of the egg and of the larva, 

 the pupa resembles the pupa 

 of the house-fly, being barrel- 

 shaped and of a chestnut- 

 brown colour; it is 5 to 5*5 

 mm. in length. The pupa 

 stage lasts from nine to thir- 

 teen days, but this period is 

 prolonged by cold. 



On emerging from the 

 pupa -case the insect has to push its way to the 

 surface of the rotting vegetation in which it has 

 been produced. This it does partly by the 

 alternate inflation and deflation of the so-called 

 ' frontal sac,' and by actively pushing forward 

 the body by means of its legs. Once on the 

 surface the insect begins to clean itself, pumps 



Fig. 42. — ^Acepha- 

 lous larva of Stomoxys 

 calcitrans. (After New- 

 stead.) 



