Hymenoptera aculeata from Majmxa and Spain. 661 



APPENDIX. 



The mimicry of Aculeata hy the Asilidm and Volucella, and 

 its 2^rohahle significance. By E. B. PouLTON. 



I HAVE already stated that I was much struck with the 

 mimetic resemblance borne by the Asilid captor to its 

 Aculeate prey on July 20, 1902 (see p, 634). The commonest 

 form of the variable female oi Dasypoyon diadcma reproduces 

 on a larger scale all the conspicuous features of Fompilus 

 viaticus : — the dark wings and the black body with a 

 reddish transverse band across the abdomen. In the case 

 of Pominhis fuscipcnnis there is not even the discrepancy 

 in size, while the resemblance in colour is in some respects 

 even closer ; for the red abdominal band is single in the 

 Fompilus, and, although spread over three segments, appears 

 to be single in the Asilid. In P. viaticus, however, the 

 three constituent bands are evident, separated as they are 

 by intervening black areas. This species of Asilid attacks 

 Aculeates far more frequently than any other kind of 

 prey. I observed it devouring small Coleoptera on several 

 occasions at La Granja, once a Hemipteron, and once the 

 male of its own species. In Switzerland I once captured 

 it with a Tachinid fly {Sarcophaga sp., Trans. Ent. Soc. 

 Lond., 1902, p. 334). On all other occasions when I have 

 observed it, including the numerous instances recorded in 

 the present memoir, the prey has been Hymenopterous — 

 almost exclusively Aculeates, but now and then Ichneu- 

 mons. The fact that the Asilid is a special enemy of the 

 group to which Fompilus belongs suggests, at first sight, 

 aggressive mimicry as the plausible interpretation of the 

 resemblance — a likeness which may be supposed to facili- 

 tate the approach of the captor to its prey. But the 

 swift and sudden swoop of an Asilid upon its victim 

 does not appear to require any accessory aid; further- 

 more, there is no evidence that Fompilus is attacked 

 above all other Aculeates. As a matter of fact this is the 

 single example I have encountered. A surer interpretation 

 of the resemblance seems to be afforded by protective 

 mimicry — a defence against insect-eating vertebrate 

 animals. The Asilid, seeking its prey, frequents places 

 where Aculeates abound, and therefore an Aculeate is for 



