40 



The flies frequent chiefly the uplands, and especially the vicinity of trees, and seem 

 to avoid water or damp localities, a fact that cattle seem to learn by experience. Owing 

 to this habit cattle that graze on meadows are generally free from them, or nearly so, 

 although those on the neighbouring hills may be attacked. 



The Sheep Bot-Fly (CepJmlcemia [CEstrus] ovis, Linn.). 



This fly, which is a great deal smaller than the ox-fly, which it 

 somewhat resembles, has a large hairy head, and ash-coloured 

 thorax, with four black lines and small black spots. 



The abdomen is light ash, more or less spotted with black. The 

 female has a tapering abdomen, with a long ovipositor, which is 

 curved forward when about to deposit the eggs. 



Mr. Riley states that this insect is the dread of sheep, in the 

 Old as well as the New AVorld, and was made mention of by a 

 Greek physician as far back as the year 560. 



" Even at the sight of this insect," says Figuier ''the sheep feels 

 the greatest terror. As soon as one of them appears the flock 

 becomes disturbed ; the sheep that is attacked shakes its head 

 Fig. 3i.-The Sheep Bot-Fly. when it feels the fly on its nostril, and at the same time strikes 

 the ground violently with its fore feet ; it then commences to 

 run here and there, holding its nose near the ground, smelling the grass, and looking 

 about anxiously to see if it is still pursued. It is to avoid the attacks of the Cephalcemia 

 that during the hot days of summer, sheep lie down with their nostrils buried in dusty 

 ruts, or stand up with their heads lowered between their fore legs, and their noses nearly 

 in contact with the ground. When these poor beasts are in the open country, they are 

 observed assembled with their nostrils against each other and very near the ground, so 

 that those which occupy the outside are alone exposed." 



According to the generally received opinion, the fly deposits an egg which hatches 

 out and climbs up the nostril of the sheep. Mr. Riley, the State Entomologist of Missouri, 

 asserts, however, that it is now an established fact that the flies deposit living maggots, 

 previously hatched in the oviduct, on the margins of the nostrils of the sheep. " On one 

 occasion." he writes, "in 1866 I myself obtained living maggots from one fly, and Mr. 

 Cockrell has since obtained over three hundred living moving worms from one fly that 

 was caught while she was after the sheep. Many flesh flies, if they cannot find suitable 

 meat or carrion on which to lay their eggs, retain these eggs so long in their bodies that 

 they hatch them into living larvae ; and it is not impossible that the above observations 

 were made with flies that had been so circumstanced, but I think it highly improbable, 

 and strongly incline to believe that it is the normal nature of this fly to produce livmg 

 larvae. I mcline the more strongly to this belief from the fact that it would be difficult 

 to attach an egg to the slimy nostrils of a sheep." 



The maggots are deposited during the early summer months, and proceed at once 

 to ascend the nostrils of the sheep by means of the hooks with which the head is furnished, 

 and by these and their continual writhing motions, they cause great irritation in their 

 passage to the frontal sinuses, where they attach themselves to the membranes which line 

 the cavities and feed upon the mucus, which is of course greatly increased by their presence. 

 The larvse remain nearly a year before reaching maturity. Mr. Verrill states that they 

 cause great inflammation and are present in large numbers, and severe illness, or even at 

 times convulsions and death result. This disease is known as "grub in the head" 



among farmers. , ^ • x • 



It has been asserted by many agricultural writers that it is ridiculous to maintain the 

 idea that sheep die from grub in the head, and many even deny that the grub is capable 

 of doing any injury to the sheep whatever, but these assertions Mr. Riley combats most 

 successfully. "If," he writes, "grub in the head be not productive of inconvenience or 

 disease, whence the suff'ering condition, the loss of appetite, the slow, weak gait, the 

 frequent coughing, the slimy and purulent matter, sometimes so profusely secreted as at 

 times to almost prevent the animal breathing ? Whence the tossing and lowering of the 

 head, and the fits of frenzy, to which so naturally quiet and gentle an animal as th^ sheep 



