AMERICAN PILOSE FLIES AND BUMBLEBEES. 271 



dimorphic in regard to this black spot. The male (PI. I., Fig. 9) 

 has a perfectly black thorax, the female has the usual black spot 

 in relation to its size and coloration like the males of V. hxmo- 

 roidalis (PI. I., Fig. 4) and V. plumata (PI. I., Figs. 6, 7). The 

 yellow spot of V. Bombylans var.flava is inherited. I had in one 

 culture (unpublished data) 6 females in Ti of V. Bombylans var. 

 flava from a female V. Bombylans var.flava (PI. I., Fig. 8). 



The V. Bombylans var. caucasica, which lives in bumblebee 

 nests of the Caucasian mountains, has a white thorax (the black 

 spot is present in the males), and the upper part of the abdomen is 

 also white, but the third to sixth abdominal rings are exactly the 

 same as in the European V. Bombylans and V. hxmoroidalis 

 (compare Figs. I, 2, 3, 4, 8, PI. I.). 



On looking at this fly one gets the impression that only the 

 yellow hairs of the European variety V. plumata and V. haemo- 

 roidalis have changed into white, but that the black and fulvous 

 hair covering the end of the abdomen remained unaffected. A 



i 



parallel color change occurs in almost all black bumblebee species 

 which inhabit the Caucasus. The Volucella Caucasica is thus 

 similar to the Caucasian B. eriophorus, B. niveatus and other 

 species of this region, which have white patches of hair on the 

 thorax. The black and rufous parts of the bumblebees' abdominal 

 rings, which correspond to the black and rufous bands of the 

 endemic Volucella flies remained also unaffected and similar in 

 coloration to those of the European Bombus lapidarius, B. 

 confusus and Volucella Bombylans (type) . Many other Caucasian 

 flies (Cheilosia cestracea, Tabanus gudaurensis, T. tricolor, etc.) 

 have similar color changes parallel to those described above. The 

 appearance of white spots or bands is characteristic for both 

 bumblebees and flies of this mountain region. 



Summarizing these data we can say that there is a striking 

 phenomenon of color convergence between European Syrphidx 

 (especially Volucella, and its varieties), Tabanidx, Asilidx and 

 (Estridx and bumblebees, which are distributed in the same 

 geographical area. A similar parallelism in coloration can be also 

 noticed for the Caucasian region. It must be also pointed out 

 that there is a predominance of certain color patterns for the 

 European group of bumblebee-like flies and bumblebees. The 

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