122 On the Preij of the Ytlhno Dang-FJy. 



but a normal-sized CaUiphora erythrocephala, after being 

 pounced upon by a Yellow Dung-fly, could hardly pass 

 unnoticed, since such a victim would be much broader and 

 bulkier thau its captor. If, therefore, as Prof. Lefroy main- 

 tains, S. stercoraria is really " a constant and general feeder 

 on the common species of Blow-fly in England throughout 

 the season,'^ the present writer feels his previous ignorance 

 of the fact to be well-nigh inexplicable ; other\vise he can 

 only regard his failure to notice even one solitary case in 

 point as due either to singialar ill-fortune, or to an invariable 

 purblindness or lack of observation far more reprehensible 

 than anything read of in our youth in the edifying tale of 

 " Eyes and No Eyes.'' Another reason for doubting 

 whether S. stercoraria preys normally and by predilection 

 ui)on C. erijthrucephala is that, as a general rule, the two 

 species do not occur together to any extent. Of course. 

 Blow-flies and Yellow Dung-flies may, and doubtless fre- 

 quently do, encounter each other in certain places, such as 

 in country gardens or on the flower-heads of Angelica, 

 Heracleum, and otlier umbelliferous plants in ditches and 

 hetlgerows ; and no one would wish to deny that under such 

 conditions an occasional Blow-fly may succumb to the 

 rapacity of its yellow-coated neighbour. Generally speaking, 

 however, CaUiphora erythrocephala does not wander far froai 

 human habitations, and is therefore not likely to come very 

 much into contact with S. stercoraria, which, as everyone is 

 aware, is most in evidence on cattle-droppings iu pasfure- 

 flelds, practically throughout the year. Even C. vomitoria, 

 L., the other British representative of the genus CaUiphora, 

 does not on the whole haunt the same spots as the Dung-fly. 



Turning to the evidence of other observers. Prof. E. 13. 

 Poulton, F.R.S., has kindly given permission for the repro- 

 duction of the following extract from a letter recently 

 received from him. " Since 1906,'' writes Prof. Poulton, 

 " further material, somewhat larger in amount, has accumu- 

 lated in the Hope Department of the University Museum, 

 Oxford, chiefly as the result of the investigations of Mr. A.. 

 H. Hamm. The prey, as in the earlier series, consisted of 

 small flies from various groups, Prof. Lefroy's conclusions 

 being partially supported by only a single example — Scaio- 

 p)haga ordinata ^ with a very small specimen of CaUiphora 

 vomitoria as its prey (Paignton, April 10, 1914). 



" There can be no doubt that the species Scatojjhago, 

 iu the wild state, rarely attack any but small flies, and 



* A species in wbicli the male is smaller and less liairy thai) in 

 »S'. stercoraria, L. — E. E. A. 



