4 BULLETIN 597, U. S. DEPARTMENT OF AGRICULTURE. 
upon the flanks or forelegs of the animal. Unlike G. intestinalis, 
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. 
Fic. 2.—Gastrophilus haemorrhoidalis: Female. The S ecies characteristics 
Qviposits only upon the small hair on the lips Ie 
of horses, preferably the portions moistened by of the eggs of the three 
saliva. Greatly enlarged. (Original.) 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 lave, as can be seen in the illustration (PI. 1), 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 larve. 
KEY FOR THE IDENTIFICATION OF FULLY “DEVELOPED LARVA: OF GASTROPHILUS SPP. 
1. Spines arranged in two alternating rows, the first more developed than the 
Seconds===a2= 9 SS SI es ee en 2 
SPOUT © Ses iT OTN eds yy TR ele sag Se pene G. nasalis. 
2. Spines long and prominent, lacking only two to three pairs on dorsal center 
CON EDT] Ae ra QUH Tt Gl alin 2X0) 9p ere eae eee ls DREN ENED SNS HORN a 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 
ho] OY sya IN OY[ELO pI ella sseeese es pee Nee en Se G. haemorrhoidalis. 
