182 INSECTS AND MAN 



twelve to eighteen, on the nostrils of sheep, or sometimes 

 having developed within the body of the fly, living larvae, 

 to the number of five or seven, are deposited in the same 

 position. The cream-coloured maggots at once proceed to 

 work their way up the nostrils and nasal passages, causing 

 intense irritation during their travels, till they reach the 

 frontal sinuses, cavities lying between and slightly above 

 the eyes. These cavities are lined with a membrane, and 

 mucus is always present in them. To the membrane the 

 maggots attach themselves by minute hooks placed on each 

 side of their heads ; on the mucus they feed. When fully 

 grown, the larvae change in colour, becoming darker 

 towards the tail end, so that they show all shades of 

 colouring, from white on the first two or three segments 

 to dark brown on the last segments, whilst a number of 

 minute brown spines, all pointing posteriorly, assist in 

 locomotion. When ready to pupate the maggots pass down 

 the sheep's nasal passages, being materially aided by violent 

 sneezing on the part of their host, and fall to the ground, 

 where they quickly bury themselves; and in forty-eight 

 hours they contract to half their original size, at the same 

 time becoming smooth, hard, and black. The pupal stage 

 lasts from forty to fifty days. 



SOME MORE PESTS OF SHEEP 



The nostril fly is not the only British dipterous parasite 

 of the sheep ; the green-bottle fly or sheep maggot, Lucilia 

 sericata, and the misnamed sheep tick or ked, Melophagus 

 ovinus, are both of considerable importance from the 

 stock-keeper's point of view. Lucilia sericata is quite 

 common in this country, whilst in Holland it often becomes 

 so numerous as to be a very serious pest. During the 

 warmer months of the year the female lays about five 

 hundred eggs, fastening them in groups of fifty or so 

 to the wool of the host, selecting, as a rule, sheep with 



