COMMON FLIES AND HOW TO TELL THEM APART 145 



parts with a tiny papilla on each side (fig. 20) and there is but one 

 great hook. The anterior spiracles (fig. 21) show six or seven lobes; 

 on the under side of the sixth and following segments there is a trans- 

 verse, swollen area, wider in the middle and somewhat pointed toward 

 each end. These areas are provided with minute teeth. The area is 

 slightly prominent and shows two approximate processes. The stigmal 

 field is barely if at all concave and not outlined by tubercles ; the posterior 

 spiracles (fig. 22) are prominent, less than their own diameter apart 

 and each with three winding slits and a button at the base. In some 

 cases two of the winding slits are apparently connected. The second- 

 stage larvae has two straight slits in each stigmal plate, while in the first 

 larval stage there are two smaller slits on a tubercle each side of the 



Fig. 20 (left). — Larva of Mmca domestica; dorsal view of head and porthorax. (Greene.) 



Fig. 21 (center). — Larva of Musca domestica; lateral view of terminal segments. 

 (Greene.) The spiracles are located on the eighth abdominal segment. The ninth 

 and tenth segments are ventral and not very distinct, enclosing the anus. 



Fig. 22 (right). — Larva of Musca domestica; enlarged sketch of right stigmal plate. 

 These plates are less than their breadth apart. (Greene.) 



middle and in this stage there are no anterior spiracles. (See Chapter 

 VIII.) 



The larva of the house fly is rarely swallowed, but there are records 

 to that effect. It sometimes breeds in decaying fruits and vegetables. 

 The principal breeding place is in horse manure. It also breeds in human 

 excrement and because of this habit it is very dangerous to human 

 beings. 



StoTTioxys calcitrans Linnseus 



The larva of this species is very similar to that of the house fly, with 

 a single great hook; the anterior spiracles have five lobes (fig. 23) ; the 

 sixth and following segments have each an area on the under side pro- 

 vided with tubercles ; this area is wider in the middle ; anal area has two 

 submedian tubercles and three each side of these; above them is a row 



