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Ageressive Mimicry Among the Flies of the 
Genus Volucella. 
UCH attention has recently been drawn to the resemblances 
which exist between the forms of Volucella and certain species 
of Hymenoptera. Not only are theoretical explanations of the 
resemblances in dispute, but there is disagreement as to the exact 
species of Bombus which are mimicked. It may therefore be oppor- 
tune to describe briefly the characters both of the Diptera and 
Hymenoptera concerned. 
In England, there occur four species of the genus Volucella ; of 
these, V. inanis, V. pellucens, and V. inflata possess a smooth or nearly 
smooth body, while V. bombylans alone possesses a markedly hairy 
body. 
V. imanis 1s parasitic in the larval condition on the larve of wasps 
and hornets; the adult in no small degree resembles a wasp. V. 
pellucens and V.imflata are similarly parasitic on wasps, but neither 
can be considered to bear a resemblance to its hosts in the adult 
stages. The larva of V. bombylans is, in the same way, parasitic on 
certain species of the genus Bombus. The adult of this last occurs. 
in two varieties; the dimorphism affects both sexes, and _ inter- 
mediate forms are occasionally found. 
The one variety is black, with the apical portion of the abdomen 
red. It thus closely resembles, both in size and colour, a small 
worker of Bombus lapidarius, or of B. derhamellus, or of B. sylvavum 
(in some of its variations). The other, var. mystacea, has a yellow 
border to the otherwise black thorax, yellow hairs on the basal portion 
of the abdomen, which is itself in this region yellow and semi-trans- 
parent, and a grey or greyish-yellow apex to the abdomen. The 
exact extent of the yellow colouration is liable to variation both on 
the thorax and abdomen. Here the resemblance is to a worker of 
such species of Bombus as B. pratorum, B. hortorum, B. schvimshivanus, 
B. tervestvis (lucorum), or B. syluavum (in other variations). The two 
varieties present also a superficial resemblance, when on the wing, 
to two other bees, viz., Authophora retusa and A. pilipes. The males of 
these two bees are clothed with brownish hairs, which fade to a 
yellowish grey in weather-beaten specimens, with a considerable 
mixture of black in certain lights; the females are entirely black 
