C. W. Johnson.
The Volucella Bombylans Group in America.
Psyche 23(6):159-163, 1916.

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PSYCHE
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VOL. XXIII DECEMBER, 1916 NO. 6
THE VOLUCELLA BOMBYLANS 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



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160 Psyche [December
only pair I ever took in cop. belonged to the two extreme forms. There can be but little doubt that the form bombylans mimics Bombus lapidarius, while the form plumata mimics Bombus terres- tris. It is only natural that with such a remarkable dimorphic species pairing indiscriminately, and mimicking a genus such as Bombus in which there are numerous other color forms, various other color variations should frequently occur, and a vast number of these have been described as distinct species or have received varietal names.
"If it be once recognized that all the European species which are densely pilose belong to one species, concerning which I hold no possible doubt, then the synonymical list in this book will answer for itself, though I may add that I possess several specimens of the North American V. fascialis Will. and I cannot distinguish any structural distinction, so that I expect both V. facialis Will. and V. evecta Walker are also synonymous." Verrall further states : "A remarkable instance of this mimicry occurs in one very common species, V. bombylans, which (I estimate without accurate observation) imitates Bombus terrestris (and its allies) for about 60 per cent., but imitates B. lapadarius for about 38 per cent., while the other 2 per cent. may be of almost any Bombus coloring."
Another interesting feature in connection with this matter is that the inquiline bee Psithyrus rupestris so closely resembles Bombus lapidarius as to be scarcely distinguishable while P. vestialis is banded similar to B. terrestris. In this country our species of Psithyrus closely resembles our species of Bombus and no species resembling P. rupestris is found here. From the above we might infer that the typical V. bombylans is absent in America because there is no bumble-bee here like the Bombus lapidarius of Europe. On the other hand our forms resemble more closely the various species of Bombus found here than the European species do. Thus we have forms with seg- ments three to five of the abdomen with entirely black pile, resembling Bombus pennsylvanicus, etc., and others with a fulvous band on the third segment resembling Bombus ternark. Regarding their habits Verrall says : " Probably all the European species of this subfamily are scavengers in the nests of large aculeate Hymenoptera, feeding on the diseased pupae, etc., but not



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19161 Johnson-The Volucella bombylans Group in America 161 parasitic on the living larvae or pups, so that the association is friendly and consequently not resented by the more powerful Hymenoptera; beyond this the scavengers have probably gradually mimicked their hosts in order to obtain the protection afforded by their aculeate powers. Dr. Sharp's observations on the larvae of V. inanis, which live in the nests of Vespa crabro, tend to show that the larvae are welcome scavengers who live on the pupae which have recently died and who thereby prevent those dead pup= from contaminating the nest, for which friendly action their imitative coloring may possibly indicate them as friends rather than conceal them as enemies."
Twenty-one specific names are placed in the synonomy by Verrall and twenty-four (including the American V. evecta, sanguinea and facialis) are in the synonomy under V. bombylans in the Katalog der palaarktischen Dipteren, 1907. I have before me seventeen specimens of the European and Asiatic forms and forty-one specimens of the American forms. Specimens from Knight Valley, Cal. (H. Edwards), described as fascialis Will. cannot be separated satisfactorily from the Euro- pean forms, plumata and hcemorrhoidalis. The pile on the pleura is black and the face and front yellow. A male from Alai Mountains, Turkestan, shows the same variation as a specimen from Califor- nia, the lateral stripe of yellow pile being absent in front of the tranverse suture; the face, however, is black and the antennae slightly darker in the Asiatic specimen. The color of the antennae used by Bigot in his table (Ann. Soc. Ent., France, July, 1883, p. 79) seems to be of little value in separating the forms as there are apparently all gradations from reddish brown to brownish black. As the typical bombylans is not known in America it is perhaps best at present to use fascialis for the American form and treat all the American forms as independent of the European. There is a form closely resembling fascialis, with the dorsum of the thorax black pilose and face yellow, but the pile on the pleura is yellow. It seems to be confined to the northeastern United States and Canada. .Before me are specimens from Franconia, N. H. (Mrs. A. T. Slosson), Wales, Me., June 20, 1909, and Lake Aziscoos, Me., July 8, 1916 (C. A. Frost), Red Indian Lake, Newfoundland, July 20, 1906 (Owen Bryant), and Lewisport, Newfoundland, July (L. P. Gratacap). To this form I assign



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162 Psyche [December
the name lateralis.
Types in the Boston Society of Natural
History, American Museum of Natural History and the author's collection. These two forms resemble Bombus terrestris moderatus and Psithyrus ashtoni.
Another form has the dorsum of the thorax more or less black pilose with the middle of the third segment of the abdomen reddish, with long reddish pile. As the latter character applies to san- guinea Will., I will adopt that name, although there is apparently a slight discrepancy in the color of the pile on the thorax. This form I have only from the Rocky Mountain region, Silver Lake, Utah, July 16; top of Las Vegas Range, 11,000 feet, end of June (T. D. A. Cockerell); top of range between Sapello and Pecos Rivers, about 11,000 feet, August (T. D. A. and W. F. Cockerell) ; Banff, Alberta, July 17, 1902 (Amer. Mus. Nat. Hist.). The reddish band across the abdomen suggests a resemblance to ~imbus ternarius, B. huntii, B. melanopygus, B. sylvicola, etc. Specimens, which have been referred to V. evecta Walker, rep- resent two quite distinct forms, the typical evecta has the face black, pile on the dorsum of the thorax entirely yellow and the abdomen with a band of yellow pile at the base and another at - the tip of the abdomen, pleura yellow pilose. The other form differs in having only a basal band of yellow, the remainder of the -
abdomen black.
To this form I give the name americana.
Types
in the Boston Society of Natural History and the author's col- lection. It resembles a number of the more characteristic species of American Bombus, including Bombus pennsylvanicus, B. affinis, B. bimaculatus, etc., and Psithyrus laboriosus. Typical specimens of evecta are in the collection of the Boston Society of Natural History from Franconia, N. H. (Mrs. A. T. Slosson), North Adams, Mass., June 14, and Sharon, Mass., June 13.
The form americana is more widely distributed. Monmouth
and Orr's Island, Me.; Hanover, N. H.; North Adams, Great Barrington, Mount Tom, and Auburndale, Mass. ; Delaware Water Gap and near Newark, N. J., and Folsom, Pa. The Labrador specimens represent an interesting form and were it not for the great variation and wide distribution of the group, I would describe it as a new species without hesitancy.



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