BULLETIN 597, U. S. DEPARTMENT OF AGRICULTURE. 



upon the flanks or forelegs of the animal. Unlike G. infest inalis, 

 it does not remain near the animal prior to the deposition of a 

 second egg. 



G. haemorrhoidalis is easily distinguished by the bright orange 

 red on the tip of the abdomen. The thorax above is olive gray and \ 

 hairy, with a black band behind the suture. The base of the abdo- 

 men is whitish and the mid- 

 dle blackish, which is in 

 strange contrast with the 

 orange red of the end. It 

 deposits only upon the small 

 hairs on the lips of horses 

 and mules. 



The males of G. intesti- 

 nalis and G. haemorrhoi- 

 dalis are often found await- 

 ing the approach of females 

 to the horses, and when they 

 arrive the flies copulate. 



The species characteristics 

 of the eggs of the three 

 species occurring in the 

 United States can best be observed by referring to the illustration 

 (fig. 3). While G. intestinalis is usually attached about one-half its 

 length to the hair, G. nasalis is attached almost its entire length. 

 G. haemorrhoidalis is always found attached to the base of a hair on 

 the lips. These hairs are so small that one does not observe them 

 with the naked eye. It is the only Gastrophilus depositing here. 

 The egg is black in color and the stalk is partially inserted in the 

 pore of the skin at the root of the hair. 



Fourth-stage lavse, as can be seen in the illustration (PI. I), vary 

 in size when fully developed. In all specimens the eleventh ring is 

 completely deprived of spines, but upon the other rings the varia- 

 tions are often misleading. However, the key given herein will 

 assist in identifying fully developed larvae. 



Key foe the Identification of Fully Developed Larv.e of Gasteophilt/s spp. 



1. Spines arranged in two alternating rows, the first more developed than the 



second 2 



Spines in one row : G. nasalis. 



2. Spines long and prominent, lacking only two to three pairs on dorsal center 



of the ninth row G. intestinalis. 



Spines short and segments prominent. Completely deprived or possessing 

 only two to three pairs of spines on either side of the dorsal center of 

 the ninth ring G. haemorrhoidalis. 



Fig. 2. — Gastrophilus haemorrhoidalis: Female. 

 Oviposits only upon the small hair on the lips 

 of horses, preferably the portions moistened by 

 saliva. Greatly enlarged. (Original.) 



