ARTICULATA. 195 
The stride (figs. 125-129) are a singular family of flies which live at 
the expense of different Mammalia, each species being generally confined 
to a single species of the latter. Among the animals subject to their attacks 
are the horse, ass, ox, various species of deer and antelope, camel, hare, and 
in Peru there is a species which attacks man under the skin. Animals 
which do not fear ordinary biting flies, often exhibit great uneasiness and 
terror at the presence of these insects. The lJarve occur in three different 
modes, some in subcutaneous tumors, as in oxen; some in the head, as that 
of the sheep; and some in the stomach, as in the horse. ‘The eggs of the 
first kind (as Gistrus bovis, fig. 129) are deposited on the skin; those of the 
second (as Cephalemyia ovis, fig. 125) within the nostrils ; and those of the 
third (as Gasterophilus equi, fig. 127) upon the hairs of those parts which 
can be reached by the tongue of the animal, or about the nostril, as in the 
case of Gasterophilus nasalis. 
The moisture and warmth of the mouth of the horse hatch the eggs of 
Gasterophilus equi, when the larva passes to the stomach with the food. 
Here it affixes itself to the inner surface by means of a pair of oral hooks, 
forming a little cavity for its head. The eggs are mostly laid in August, 
and the larva remains upon the stomach until the next summer, when it is 
an inch long. It now detaches itself and is passed through the intestines, 
when it becomes a pupa in the ground, and in the course of a few weeks 
it emerges as afly. The male dies after fecundation, and the female after 
depositing her fifty or a hundred eggs. The larve sometimes affix them- 
selves to the windpipe, or pass on to the smal] intestines, when a horse is 
apt to die from the irritation, and in a few cases they perforate the 
stomach. In most cases the presence of bots (as these larvae are named) 
causes no injury to a horse, and their head is so deeply imbedded that 
no medicine sufficiently active for their expulsion can be administered with 
safety. 
The presence of Cephalemyia ovis, or the fly of the sheep, puts the 
animals to flight and causes them to huddle together upon some sandy or 
bare spot (as if to prevent the fly from having a resting place), with their 
heads down and turned together, and their feet in continual motion to keep 
it from effecting its object. The fly, however, by a rapid dart, reaches the 
nostril, where it deposits an egg, the larva of which ascends the nostril, 
causing great uneasiness to the sheep, which runs around with every 
mark of distress. The larva makes its way to the frontal sinus, the 
anirum, or the nasal bones, where it affixes itself with its oral hooks, 
and remains until the next spring, when it crawls out and enters the 
ground tochange. It remains in the earth six or eight weeks in the pupa 
state, and when it becomes an imago it is as short-lived as the horse bot-fly. 
The Gfstrus bovis, the larva of which lives beneath the skin of the back 
im oxen, causes great terror among these animals, which run for pro- 
tection to bodies of water. The larve of strus tarandi (fig. 128) are 
found under the skin of the reindeer. Another member of the family 
iniests the frontal sinus, throat, and mouth (under the tongue) of the same 
animal. 
399 
