THE SVRPHIDAE OF OHIO 49 



On the bodies of these flies the vestiture is, I believe, responsible, 

 almost exclusivel}', for the carrying of pollen. In this respect the species 

 vary widely from almost bare to very densely' pilose, and, as pointed out 

 by Dr. Smith (I. c), this vestiture is often composed of spurred and 

 branched hairs (Plate VIII, Fig. 159). In general the more thickly 

 pilose species carry more pollen. Many of such specimens in collections 

 have the body thickly dusted with pollen grains. 



By the feeding habit of the fly I mean, whether it ordinarily visits 

 flower after flower on the same plant, or flies more or less directly from 

 one flower to another of the same kind on another plant. I have often 

 noted individuals hovering about the same plant and feeding on flower 

 after flower. If the other habit is followed in any case cross-fertilization 

 would be much more apt to be secured. 



Relations to other Insects. The adults enter into no particularly close 

 relations with other insects that I know of except with those Hymenop- 

 tera which certain of them mimic. If the theory of protective mimicry 

 has any real significance it must result in endangering by so much the 

 mimicked form. That is, wdiile one predaceous enemy is learning from 

 his attack on the fortified bee to avoid prey of that appearance, another 

 may be experiencing a successful and pleasant attack on the defenseless 

 fly of similar appearance. Thus the value of the warning mark to both 

 bee and fly is lessened in direct proportion to the number of defenseless 

 individuals bearing it. (See also pp. 35-37.) 



It is interesting to note the attitude of those Hymcnoptcra, in whose 

 nests the larvae of Microdon and ]"oliicella live, tow^ard the adults of these 

 flies. Volucclla, according to reports, meets with no resistance or antago- 

 nism. The adults of Microdon, however, are treated with great animosity 

 by the ants among which they spent their immature stages. The ants 

 seize the teneral adults and lick them until the formic acid secreted b\- the 

 ants kills the flies. Wheeler believes that the habit of the larvae of pupat- 

 ing in the superficial galleries of the ne.st, and of the adults of emerging 

 at night, when ants are more or less torpid, are adaptations to making it 

 as ea.sy as possible for the adult flies to escape. 



Relation to other Animals. It seems probal)lc that the adults of 

 many species of Syrp/u'dac are a considerable source of food for insectivo- 

 rous animals of all kinds, especially birds and Ami)hibians. The king-bird, 

 phoebe and flicker are known to feed on liristalis tcua.w but I am not 

 able to give much detailed data on this point. 



