INSECT ENEMIES OF LIVE STOCK 181 



lineata are not unlike honey bees in general appearance, 

 half an inch long, and of a general black colour, furnished 

 with yellowish, reddish, and black hairs; bovis is much 

 larger, and is banded with yellow and black. 



Another (Estrid which deserves mention, on account of 

 its peculiar, if repulsive habits, is the emasculating bot fly, 

 Cuterebra emasculator, of North America. The life-history 

 of this fly is but little known. Exactly when and where 

 the eggs are laid is a mystery, but the larvae develop 

 within the scrotum of grey squirrels, red squirrels, and 

 chipmunks, and, in doing so, destroy the testicles, hence 

 the popular name of the fly. The larvae, having attained 

 full development during the months of August to October, 

 escape to the ground to pupate, and remain in the pupal 

 stage till July of the following year. The life-cycle, 

 therefore, takes at least two years to complete. The 

 damage done by this fly appears to be somewhat local, but, 

 should it be allowed to spread and increase, the harm done 

 to the fur trade might, conceivably, be considerable. 



The sheep bot fly, (Estrus ovis (fig. 50), popularly named 

 the nostril fly, has been known for centuries ; in fact, it was 

 mentioned by the Greek physician Alexandra Trallian in 

 the year 560. The fly itself resembles a large house fly in 

 appearance. The upper parts of its head and thorax are 

 dull yellow, though they appear brown, owing to being 

 covered with little round spots. The abdomen of five 

 segments is velvety and variegated with dark brown and 

 straw colour above, whilst the underside has a dark spot 

 in the middle of each segment, in place of the variegation. 

 The head, which is white below, is furnished with very 

 small antennae, purplish-brown eyes, and three small 

 eyelets. There is no mouth, and the only instinct of the 

 adult fly seems to be to continue its kind. It is very lazy, 

 except when attempting to deposit eggs, which it does 

 very soon after fertilisation has taken place. 



The characteristic, curved eggs are laid in clusters of 



