1894.] 177 



ON MIMICRY IN DIPTEEA. 

 BT COLBEAN J. WAINWEIGHT, 



When collecting Diptera on the sallows at Wyre Forest during 

 the last Easter holidays, I came across some cases of mimicry which, to- 

 gether with some conclusions suggested by them, I think worthy of 

 notice. I obtained several each of Cheilosia grossa and flavicornis, 

 two very similar but distinct species belonging to the Family 8yr- 

 phidcB, both of which seem remarkably partial to the sallows, where 

 alone we found them. I was particularly anxious to get these two 

 species, but had a great deal of difficulty in distinguishing them from 

 the bees of the genus Andrena, many of which were on the blossom ; 

 they particularly resembled Andrena fulva, and we netted far more of 

 the bee than of the Uipteron, in our efforts to get the latter. The 

 resemblance is very strong, colour, size and (to a considerable extent) 

 shape being much the same ; when at rest on a flower the Dipteron 

 curls its body under a little, as the bee does, and folds its wings over 

 its back in the same manner, in fact, these two species {grossa and 

 flavicornis) are undoubtedly very good mimics of the bees. 



In addition to the Cheilosics, we also took a large number of an 

 EcTiinomyia, probably ursina, one of the Tachinidce. This was very 

 common throughout the Forest, but specially so upon the sallows. It 

 was easily distinguished when once its presence was known, although 

 it had a distinctly bee-like appearance, unlike the other species of 

 EcJiinomyia with which I am familiar. It, however, resembled no 

 species in particular ; it bore a general resemblance to Bonibus musco- 

 rum in size, shape and colour, but it was not so hairy, and it did not 

 fold its wings bee-fashion, but kept them fully extended in the well- 

 known fashion of many of the Muscidce, and so would fail to deceive 

 the eyes of an entomologist. 



There is very little doubt that in the spring, when insects are not 

 very numerous, and when, therefore, we may reasonably infer that 

 their enemies are unusually alert in discovering and capturing them, 

 that it must be even more necessary than during the summer, for those 

 insects which do appear, to be well protected in some way from their 

 foes, and especially if they happen to be species which, through feeble 

 reproductive powers or other similar causes, are limited in numbers to 

 commence with. Now, the two Cheilosics are distinctly species which 

 are limited in numbers, in fact, they are somewhat rare species, and 

 may be described as occurring singly ; they are not robust species, in 

 fact, rather the reverse, and therefore, they are just such species onr 



