1904.] 



The Sheep Nostril Fey. 



229 



fly maturing under the cover of the last moulted dark-coloured 

 skin of the mature larva. The flies are found at work in the 

 summer months, and the length of larval life is given at nine 

 or ten months. The number of maggots in a head varies, but 

 a small number is commoner than a large ; maggots of very 

 different sizes and in different stages of development may be 

 found at the same time in the same head. 



The following quotation of Bracy-Clarks, from the 1797 

 Volume of the Linnaean Society's Transactions, describes the 



Section of Sheep's Nostril (after Curtice). 



behaviour of the sheep when their enemy is at work : — " The 

 moment the fly touches the nose of the sheep they shake their 

 heads and strike the ground violently with their forefeet, at the 

 same time holding their noses close to the earth, they run away, 

 looking about them on every side to see if the fly pursues ; they 

 also smell to the grass as they go lest one should be lying in 

 wait for them. If they observe one they gallop back or take 

 some other direction. As they cannot, like the horses, take 

 refuge in the water, they have recourse to a rut, dry dusty road 

 or gravel-pits, where they crowd together during the heat of the 



