236 DIPTEEA OR TRUE FLIES. 



The Sheep Xasal-fly (CEstrds ovis). 



Sheep are often seen shaking their heads and stamping on the 

 ground ; at other times running about with their noses close to 

 the grass. These are symptocns that CEstrusovin is about, ready 

 to deposit its eggs or young. The fly appears in the summer ; 

 it is a dull-coloured insect, which we often see in sheep districts 

 at rest at dusk, and in cold weather on the sheep-pens and 

 hovels near the sheep. The female may deposit living young 

 or ova on the sheep's nose, and the maggots crawl up the 

 mucous membrane and some enter the sinus of the head. The 

 majority live in the nasal passages, and when mature are 

 thrown out on to the grass during one of the violent fits of 

 sneezing that they often occasion by the irritation of the 

 mucous membrane. The puparia are found, like those of the 

 ox-bot, beneath some shelter on the ground. Many of the 

 bots in the sinus cannot escape, and thus die. On one occa- 

 sion the author extracted from the cerebral hemisphere a larva 

 of the fly, it probably having entered through the cribriform 

 plate of the ethmoid bone ; in another cas(! one was found in 

 the trachea. Sheep when suflering from this pest shake their 

 heads and wander restlessly about, and present some of the 

 symptoms of Sturdy. The disease for this reason is called 

 Talse-Gid ; it can be told from true Gid (Ccenurus cerehralis) 

 by the copious mucous discharge from the nostrils, and the 

 absence of that rotatory movement seen in sheep suffering from 

 Sturdy. 



Prevention and Treatment consist in warding off the fly 

 attack by either placing some substance on the sheep's nose 

 every now and then, such as strong smelling oils, removing 

 them for a year from pastures that are known to be con- 

 taminated with the puparia, and placing salt in tarred boxes, 

 so that the sheep get the creosote on their noses whilst 

 licking the salt. 



