Aggressive Mimicry Among the Flies of the 

 Gemis Vohicella. 



UCH attention has recently been drawn to the resemblances 

 which exist between the forms of Volncella 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 Volncella ; of 

 these, V. iiinnis, V. pellucens, and V. inflata possess a smooth or nearly 

 smooth body, while V. bomhylans alone possesses a markedly hairy 

 body. 



V. inanis is parasitic in the larval condition on the larvae of wasps 

 and hornets ; the adult in no small degree resembles a wasp. V. 

 pellucens and V. inflata 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. bomhylans is, in the same way, parasitic on 

 certain species of the genus Bonibiis. 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. deyhamellus, 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 che 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. pvatoyum, B. hortoyum, B. schyinishiyanus, 

 B. teyycsiris (lucoyuin), or B. sylvayum (in other variations). The two 

 varieties present also a superficial resemblance, when on the wing, 

 to two other bees, viz., Anthophoya yctusa and A. pilipcs. 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 aie entirely black 



