jAN,i893. AGGRESSIVE MIMICRY AMONG FLIES. 55 



But it is rather in size, and especially in mode of tiight, that 

 V. bomhylans resembles the Anthophovct. In both cases the insects 

 have a dashing impetuous habit, interrupted by periods of hovering. 

 During such rapid movements exact markings fail to catch the eye, 

 and the general impression produced by the two is by no means 

 dissimilar. 



It is further maintained by some observers that var. mystacea 

 resembles B. miiscoviini. This bee has tawny yellow hairs on the 

 thorax, while on the abdomen the hairs are yellow, more or less 

 mixed with black, or even entirely black. Whether mimicry can be 

 said to exist in this case is a matter of opinion, but it should be borne 

 in mind that both B. muscoviim and the mystacea variety of V . bomhylans 

 vary in appearance and colour-effect, according to the direction from 

 which they are observed. A freshly-emerged mystacea, if viewed from 

 in front, and from a low elevation, would probably be considered by 

 very many persons to resemble B. muscoviim, while, if viewed either 

 from directly above or from behind, the resemblance would probably 

 be denied. Moreover, a faded specimen of muscoriim loses much of 

 the tawny colouring and appears of a yellowish grey. 



Both varieties of V . bomhylans have been observed to emerge from 

 nests of the three species oi Bomhns which are chiefly attacked, viz., 

 B. muscovnm, B. lapidaviiis, and B. Iiortonim. The first-named of these 

 is apparently the most infested. In this connection the habits and 

 demeanour of the bees are of interest. B. miiscoviim constructs a nest 

 on or near the surface of the ground, and is of a comparatively mild 

 and paciiic disposition. The other two construct their nests at some 

 depth from the surface, and are, especially lapiclaviiis, fiercely irritable. 

 Thus the nest of muscoviim is clearly more accessible to VoliiccUa on 

 account both of the weakness of its strategic position and the faint 

 heart of the defenders. 



Be this as it may, it is exceedingly difficult to comprehend how 

 the colour of Volucella can in any way impose upon any of the bees, 

 for so soon as the fly has entered the approach to the nest it must be 

 in more or less total darkness, and from that moment the value of 

 mere colour and markings is reduced to nil. Any Bomhns which 

 encountered a Volucella in the darkness could not by any possibility 

 discriminate by the sense of sight between friend or foe. It seems 

 far more probable that the hairiness of V. bomhylans (in both varieties) 

 is the feature which should be spoken of as an example of " aggressive 

 mimicry." It is the sense of touch which alone can enable the Bombiis 

 to detect V. bomhylans in the semi-darkness, and surely the hairy body 

 is less likely to arouse suspicion when touched than would a smooth 

 body, for the latter could in no case enter the nest of Bomhus as 

 belonging to one of the natural members of the colony. 



This contention derives much support from the fact that the 

 other three species of Volucella mentioned above have hairless bodies 

 and are parasitic upon hairless Hymenoptera. Our knowledge at 



