Prey of the Yellow Dung-Fly. 119 



Lefroj' remarks that observations made by liim "show tliat 

 while the fly preys on a large variety of Diptera, it specially 

 attacks Calliphora and Musca." He states further that 

 S. stercoraria is " a constant and geaeral feeder on the 

 common species of Blow-fly in England throughout the 

 season/' and he considers it to be ''the most important 

 direct enemy of the adult fly, a check which appears to be 

 very eff'ective in this country." Prof. Lefroy proceeds to 

 explain that the author of the paper " investigated the best 

 means of transporting this species to countries where 

 Blow-fly is a serious pest to sheep, in the hope that it might 

 be possible to utilise it as a check on Blow-fly." '' This 

 has not beeu possible as yet/' writes Prof. Lefroy, '' but the 

 species seems to have much value in this connection, and 



it is to be hoped it will eventually be made use of." 



Anyone who knows anything of the importance and pre- 

 valence of the Sheep Blow-fly pest in Australia is Avell aware 

 of the urgent necessity of discovering an eff'ective remedy. 

 If S. stercoraria, a hardy and fairly prolific predaceous 

 Dipteron, does indeed feed by preference upon Blow-fiies, and 

 if it can be relied upon, without any kind of adventitious aid 

 and under natural conditions, always to attack and desti'oy 

 Calliphora erythrocephala (the Common Blow-flv) at sight. 

 Prof. Lefroy by suggesting its introduction has not only 

 gone a long way towards solving the problem at issue, but 

 has established a just claim to the gratitude of every sheep 

 farmer in the Commonwealth. While it is obvious that, 

 before any predaceous insect can be regarded as even a 

 " possible " check upon an insect pest, it must be shown that 

 the normal relations between the two are not unlike those 

 between the domestic cat and the common mouse, it Avould 

 seem to be a legitimate deduction from the remarks of 

 Prof. Lefroy quoted above that, in England, the Yellow^ 

 Dung-fly behaves towards the Common Blow-fly in the 

 manner just indicated. 



Let us, however, biiefly examine the available evidence 

 as to the feeding-habits of S. stercoraria, and in particular 

 let us see how far the experience of other observers is in 

 agreement with that of Prof. Lefroy, whose statements have 

 already been reproduced. Prof. Lefroy's original obser- 

 vations on the subject, at any rate, seem to liave been made 

 under artificial rather than under natural conditions, since 

 1)6 writes: — ''The Yellow Dung-fly first showed itself in 

 our work at the Zoological Society in 1915 in connection 

 with methods of trapping flies : it came in numbers, per- 

 sistently eating the adult Blow-flics, and scriou>ly interfered 



