ARTICULATA. 195 



The (EstridcB {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 attack? 

 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 larvae 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 CEstrus 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 aflixes 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 a fly. The male dies after fecundation, and the female after 

 depositing her fifty or a hundred eggs. The larvae sometimes affix them- 

 selves to the windpipe, or pass on to the small intestines, when a horse is 

 apt to die from the irritation, and in a few cases they perforate tne 

 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 

 antrum, 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 to change. It remains in the earth six or eigh.t weeks in the pupa 

 state, and when it becomes an imago it is as short-lived as the horse bot-fly. 



The Oestrus hovis, the larva of which lives beneath the skin of the back 

 in oxen, causes great terror, among these animals, which run for pro- 

 tection to bodies of water. The larvae of CEstrus tarandi {fig. 128) are 

 found under the skin of the reindeer. Another member of the family 

 infests the frontal sinus, throat, and mouth (under the tongue) of the same 

 animal. 



399 



