SYRPHIDAE OF MAINE. 219 



In this connection, I wish to emphasize the practical impos- 

 sibility, at our present state of published knowledge, of referring 

 larvae found in such circumstances to a definite species, or even 

 to the genus, unless specimens are reared to the adult. It seems 

 to be the custom to refer any rat-tailed larva to Eristalis tenax, 

 or at least to the genus Eristalis. Such records, unless based on 

 adults reared from the larvae, must, it seems to me, be discarded 

 as of no specific importance. I am working on the problem of 

 separating these different species in the larval stage, and have 

 examined a dozen species of rat-tailed larvae belonging to sev- 

 eral genera, the separation of which is exceedingly puzzling 

 ;and difficult, and any one of which might easily be mistaken for 

 the larva of Eristalis tenax. 



Other biological relations of the larvae, of more or less eco- 

 nomic importance, may arise from their association with other 

 insects, in aphid colonies, or in the nests of colonial insects; 

 and with their predaceous and parasitic enemies. 



ECONOMIC IMPORTANCE OF THE ADULTS. 



While the principal economic importance of Syrphidae arises 

 from the habits of the larvae, the adults are by no means devoid 

 of importance in this respect. The adults, so far as known, 

 feed almost exclusively on the nectar and pollen of flowers or 

 the honey-dew of insects. Anyone who has observed the tre- 

 mendous numbers of these flies which mingle with Hymenoptera 

 about all sorts of melliferous flowers, will be able to appreciate 

 their importance in the crjoss- fertilization of entomophilous 

 plants. All sorts of fruit and shade trees, wild and cultivated 

 flowers, and certain field and garden crops, are regularly visited 

 by these flies. Some of the flies, which possess an abundant 

 vestiture, often of spurred and branched hairs, are very admir- 

 ably adapted for the carrying of pollen. This is a subject deserv- 

 ing of careful observation. But in the absence of much definite 

 data it seems safe to ascribe to this family a very large share of 

 credit for this beneficient work, which is usually attributed to 

 Hymenoptera alone. 



