204 THE BLOW-FLIES 



The full-grown larva may measure as much as 18 mm. in 

 length. There are two distinct mandibular sclerites. The anterior 

 spiracular processes (fig. 91 D) are usually nine lobed. The posterior 

 extremity is surrounded by six pairs of tubercles arranged as shown 

 in fig. 91 ; there is also a pair of anal tubercles. The posterior 

 spiracles (fig. 91 C) are circular in shape and contain three straight 

 slit-like apertures. In the second larval instar there are only two 

 slits in each of the posterior spiracles (fig. 91 5) and in the first 

 larval instar each of the posterior spiracles (fig. 91 A) consists of 

 a pair of small slit-like orifices. 



C. eri/throcephala is an out-door fly, but it fi-equently enters 

 houses in search of material upon which to deposit its eggs, and 

 also for shelter. From its habit of frequenting faeces, which may 

 often be observed, especially in insanitary courtyards and similar 

 places, it is not improbable that it occasionally may bear intestinal 

 bacilli on its appendages or body or internally, and thus carry infec- 

 tion. Its flesh-seeking habits may also render it liable to carry the 

 bacilli of anthrax should it have access to infected flesh, and such 

 meat-seeking habits render the ingestion of the larvae into the 

 human digestive system extremely possible. Buchanan (1907) 

 recovered the bacillus of swine fever from blow-flies which were 

 caught on the carcases of pigs which had died of swine fever. 

 Further infection experiments with C. eri/throcephala are discussed 

 in a later chapter. 



The Sheep Maggot or "Green Bottle" Fly, 

 luoilia caesar l. 



This fly is an out-door species which is sometimes found in 

 houses, into which it is generally driven by adverse weather con- 

 ditions for the pvirpose of shelter. It is more commonly found in 

 farm and country houses. Although it is not so large as G. eri/thro- 

 cephala, being more similar in size to 31. domestica, it is frequently 

 called a " blue bottle " and is often referred to as the " green 

 bottle " fly. The colouring is more brilliant than that of C. erythro- 

 cephala, being of a burnished gold, sometimes bluish appearance 

 and sometimes of a shining green colour. 



The flies are usually found on dead animals and carrion ; they 

 also occur on the excrement of man and other animals. On all 



