204 



on account of the likelihood of bacterial invasion taking place during these 

 operations. 



Woodburn (in Cooper, 1913, p. 50) stated that ewes, lambs, weaners, and 

 merino sheep (especially if wrinkled) were more liable to attack than plain- 

 bodied sheep, and that wethers were less affected than ewes. He published a 

 table of percentages. Out of 6,000 weaners, merino ewes showed a loss of 

 40 per cent., merino wethers 3 per cent., Lincoln-merino crossbred ewes 15 per 

 cent., and crossbred wethers nil. 



One possible method of controlling the problem may be the breeding 

 either of crossbreds or of a merino devoid of a wrinkled skin and of heavy 

 wool on the rump region. This would more or less obviate the necessity for 

 crutching sheep. The Queensland Blowfly Committee, in a pamphlet issued in 

 December, 1920, stated that sick or worm-infested sheep are more susceptible 

 to fly attack than are healthy animals ; hence, any measures which tend to 

 restore such sheep to a normal condition are of distinct advantage. It might 

 be emphasized that any circumstances wdiich set up diarrhoea favour fly attack 

 through the greater likelihood of fouling the wool and causing it to become 

 attractive to the fly. 



It is important that the biology of the various blowflies, especially the larval 

 stages and the breeding habits should be known, as such knowledge may indicate 

 a vulnerable point of attack. It is known that all blowflies which attack sheep, 

 normally breed in decomposing animal matter, though some of them can be 

 induced to breed in decomposing vegetation also (e.g., the writer has bred the 

 common AnastcUorhina flies by transferring the young larvae from meat to horse 

 manure), but the latter material is not visited by such flies for breeding pur- 

 poses. The writer agrees with Froggatt in insisting that the most important 

 measure against blowflies is the systematic destruction of all carrion, offal, or 

 animal debris which are the normal breeding places of such flies. It is the only 

 way to strike at the root of the problem. Such destruction may be brought 

 about by burning or by thorough poisoning, as well as by encouraging the pro- 

 pagation of insectivorous birds (Froggatt and Froggatt, 1914, p. 753). 



It has been asserted that the wholesale poisoning of rabbits by means of 

 poison carts, poisoning water supplies, etc., and of dingoes and wild dogs by 

 poisoned baits, has been responsible for the enormous increase in the blowfly 

 population ; firstly, by affording additional breeding places ; and secondly, by 

 causing heavy mortality amongst insectivorous birds, lizards, etc., through feeding 

 on poisoned material. This view is not supported by McLeod and Holme (in 

 Cooper, 1913, p. 55). 



A certain amount of information regarding the duration of the ^-arious 

 stages {^gg, larva, pupa) of the chief blowflies was published from time to 

 time by Froggatt and Froggatt, while detailed systematic observations were 

 carried out in Brisbane in my laboratory, and in addition the longevity of adults 

 in captivity was ascertained (Johnston, 1921, 1922; Johnston and Tiegs, 1922; 

 Johnston and Hardy, 1923). In the present paper it is not necessary to repeat 

 the information published therein. J. L. Froggatt (1918) has given an account 

 of the spiracles of the larvae of the six main sheep maggot-flies. 



It is highly important for the pastoralist to know how far blowflies may 

 travel, as indicating the possible source of infestation. No data have been 

 published regarding Australian experience, but the writer has summarized the 

 results of Bishopp and Laake's work in Texas, which showed that species of 

 some of the genera to which certain Australian blowflies belong, are able to 

 fly, at least, eight miles, even up to 10 miles, within two days (lohnston, 1922. 

 p. 275). 



Trapping of flies has been widely advocated and figures of traps have been 

 published by Froggatt, but Russell (Editor, 1921, p. 251) regarded it as being 



