114 MISC. PUBLICATION 631, U. S. DEPT. OF AGRICULTURE 



distance somewhat less than the diameter of the spherical third 

 segment. The clypeus is depressed above, forming two pits below 

 the antennae which are strongly confluent. The proboscis and palpi 

 are reduced to three buttonlike structures; the proboscis is directed 

 backward, but does not extend between the palpi (fig. 61). The legs 

 are short. For the characteristic wing venation, see figure 62; vein 

 r-m joins the discal cell at more than half its length; vein m 3 arises 

 much nearer to the cubitulus than to the cross vein r-m; the petiole 

 of the apical cell curves more or less strongly upward. The abdomen 

 is moderately robust and not especially flattened; the sternites are- 

 broad and rectangular, and the venter is distinctly haired below. 



Life Histories. — The larvae are normally parasitic on sheep, goats, 

 and antelopes; occasionally those of one species, Oestrus ovis, attack 

 man. First-stage larvae are produced alive. They are deposited 



larva 



Anterior end ; 



Figure 60. — Rhinoestrus purpureas, first-stage - 



posterior end. (Redrawn from Portchinsky (117).) 



around the nose of the host. Subsequently, they enter the nasal pass- 

 ages and finally make their way into the frontal sinuses. At maturity 

 they leave the body of the host and drop to the ground to pupate. 



Larva. — The third-stage larva can be distinguished from those of 

 other genera by the following combination of characters: The an- 

 tennae are short and thick, and each bears two ocelli. The ventral 

 surfaces of the segments are extensively provided with small spinules ; 

 these are absent on the dorsum, except in one species not included 

 in this work. The posterior spiracles are D-shaped and completely 

 enclose the button; a transverse suture extends from the button to 

 the inner margin of the spiracle. The postanal swelling bears a pair 

 of conical lateral protuberances. 



OESTRUS OVIS Linnaeus 



The Sheep Bot ; "Grub-in-the-Head" 

 (Fig. 62) 



Synonym. — Cephalemyia (or Cephalomyia) ovis (Linnaeus). 



Recognition Characters. — Adult (fig. 61) : The head is yellowish, the de- 

 pressed pocklike pits of the parafrontals and the third antennal segments being 

 black ; the frontalia are on a level with the parafrontals. The pits of each para- 

 frontal are rather deep and numerous, the number of those bordering the frontalia 

 being about 12. The thorax is covered with a grayish bloom, the black back- 

 ground exposed in the form of 4 stripes ; the bloom is interrupted by numerous 



