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In parts of South Africa and in Australia, species of Pycnosoma 

 (Chrysomyia) are known to blow sheep, and in the latter country are now 

 regarded as the chief cause of such myiasis. Patton, however, has stated that 

 these flies in the final maggot stage are predators on the larvae of other blow- 

 flies ; hence the possibility that others may initiate the attack and the "hairy 

 maggots" may actually be present (at least in part) in the role of destroyers of 

 the culprits, and as a consequence the flies bred out from such infested wool 

 would be chiefly Pycnosoma. This point has not been cleared up yet. The 

 writer has bred the two "hairy maggots" in abundance from carrion, but the 

 larvae of other blowflies were also present as a rule, and it is probable that 

 Pycnosoma is present on sheep in the dual role of carrion feeder and predator. 



Froggatt has frequently drawn attention to the change of habit in the case 

 of these various blowflies which were at first carrion feeders, the adults depositing 

 eggs or larvae on or in dead animals, and ultimately coming to attack wool on 

 living sheep. The writer of the present article does not see any reason to 

 assume a change of habit. Flies are readily attracted to those places where 

 bacterial decomposition is going on and oviposition is stimulated. Soiled wool 

 contains abundant bacteria and a chemotropic influence is soon sufficiently pro- 

 nounced to attract pregnant blowflies, which deposit their eggs or larvae on the 

 wool. In part of the area in which larval activity is first manifested there will 

 commonly be noticed a more or less pronounced greenish discolouration, no 

 doubt caused by bacterial agency, which is secondarily augmented by the pre- 

 sence of the maggots. This seems to pave the way for the larvae which are 

 then feeding in dead and decomposing wool and foreign material until such 

 time as they reach the skin, when the irritation caused by their presence, and 

 probably also the attempts of the sheep to dislodge them, may lead to a breaking 

 of the skin on the fevered part, bacterial infection of the injury soon occurring 

 when the maggots are thereby able to get inside the damaged tissue. If this 

 view be correct, then one very important line of attack against sheep myiasis 

 would be to check bacterial activity. According to an article in the Australian 

 daily Press during last December, Dr. W. Sinclair advocates using a solution 

 containing one part of mercury in 500,000, which, he claims, is taken up from 

 the skin, enters the blood, and becomes excreted through the sweat and yolk 

 glands, reaching the wool and skin, where bacterial invasion is then checked ; 

 but if sheep be already blown and the skin broken, then direct application to the 

 moist area is needed, when the bacteria are destroyed, the maggots drop off, and 

 the wound soon heals. The method has not, as far as I know, been fully 

 investigated. 



There are certainly predisposing factors towards fly attack. It has been 

 pointed out by Froggatt (1905, 1913, 1915, 1922) that the sheep breeder has 

 changed the character of the Australian merino by making practically every part 

 of the animal produce wool, and even by encouraging the development of a 

 wrinkled skin in order to give a greater wool-producing surface. Hence the 

 wool is extremely fine and dense, and even the rump portion, which is so readily 

 soiled, now carries a mass of wool. "This artificial increase in weight, quantity, 

 and fineness of wool is accompanied, too, by an increased secretion of yolk, 

 which, rising from the skin and spreading all through the wool fibre, forms an 

 additional attraction for the flies and supplies food for the maggots" (Froggatt, 

 1922). Any circumstance which causes diarrhoea favours fly attack, as also 

 does the act of lambing, merely through soiling the wool of the breech of the 

 animals. Even urine may bring about a similar result, and once such dense 

 wool becomes infested, the maggots are soon able to work their way into the 

 warm, moist, bacteria-laden wool and pass through their stages under optimum 

 conditions. The docking and marking of lambs gives flies a further opportunity 



