Hymenoptera aculeata from Majorca and Spain. 661 
APPENDIX. 
The mimicry of Aculeata by the Asilide and Volucella, and 
ats probable significance. By K, 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 of Dasypogon diadema reproduces 
on a larger scale all the conspicuous features of Pompilus 
viaticus :—the dark wings and the black body with a 
reddish transverse band across the abdomen. In the case 
of Pompilus fuscipennis 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 
Pompilus, 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 Pompilus 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 Pompilus is attacked 
above all other Aculeates. As a matter of fact this is the 
single example Ihave 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 
