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PSYCHE rf^m^ 



VOL. XXIII DECEMBER, 1916 



THE VOLUCELLA BOM BY LANS GROUP IN AMERICA. 



By Charles W. Johnson, 

 Boston Society of Natural History, Boston, Massachusetts. 



Among some Labrador Diptera received from the Museum of 

 Comparative Zoology for study through the kindness of Mr. 

 Samuel Henshaw, was a form of Volucella belonging to this 

 interesting group. The work of identifying this form compelled 

 me to make a study of the entire series, and the following notes 

 are brought together in the hope of creating an interest in the 

 study of this group in America, and possibly showing their com- 

 mensal relations with the various species of genus Bombus, as has 

 been done in Europe. 



To ignore the various forms however slight without defining 

 their limits, even though intermediates apparently exist, does not 

 simplify matters in this case. To clearly show their differences 

 and their resemblances to their apparent hosts — the various 

 species of Bombus — seems to be the first step to be taken in a 

 provisional study. 



The group probably represents a protean species, of common 

 origen, circumboreal in distribution, and representing an extremely 

 interesting case of resemblance or "mimicry" of their hosts, the 

 bumble-bees. If what is true of the European species is also 

 true of the American forms, they offer a fascinating field for 

 research. 



In referring to their resemblance to various species of Bombus, 

 Verrall in British Flies, Vol. 8, page 485, 1901, says: 



"This species varies infinitely in the color of the pubescence 

 between the two common forms which I have noticed above; 

 these two forms are so remarkably distinct that nobody would 

 imagine at first that they belonged to the same species, but they 

 are now well known to occur and to pair indiscriminately. The 



