SYNOPSIS OF NORTH AMERICAN SYRPHID^. 271 



This function is that of the inflatable face, and hence it is, this part of 

 the Syrphid anatomy is one of the very best for the furnishing of struct- 

 ural characters in the adult fly. 



So far, the larvae have furnished evidence of only two principal groups 

 in the family. In the one {Eristalince) the larvte have no mouth-hook- 

 lets, and in general only rudimentary mouth-parts {EristaUs, Mallotay 

 Volucella, Selop/iilus, Focota, Xylota, Orthoneura) ; in the other the 

 larvae are provided with well developed mouth-hooklets {Syrphus, Chi- 

 losia, Doros, Baccha, Merodon, and others). This division coincides 

 fairly well with that based upon adult characters, but a classification 

 drawn from the earlier characters can rarely supersede that founded 

 upon the mature ones, though it may materially modify it. Certainly 

 Orthoneura cannot be placed among the Uristalince, or Merodon among 

 the Syrphince without doing violence to most important and real relation- 

 ships. Brauer thinks that the larvsB, when they are more studied, will 

 furnish more natural groups in the Syrj^hidse, but I do not agree with 

 him, at least to any more than a limited extent. The perfect insect is 

 the most complex, and must offer a greater number and more diverse 

 characters than the simpler stages can jjresent. The use which larval 

 characters subserve the individual or species must first be ascertained 

 before we can learn their true value. It is not at all probable that the 

 possession of mouth-hooklets can materially modify the life-habits of 

 a species when they are present or absent in such related forms as 

 Chilosia and Orthoneura. To insist upon a classification based upon 

 such characters, would be like insisting upon an equal valuation for 

 the presence or absence of palpi, ocelli, etc. The presence or absence 

 of mouth-hooklets cannot be used to divide the family into principal 

 groups. 



The principal genera in which the larval habits are known are the fol- 

 lowing : 



Baccha, Syrphus, Sphcerophoria, Pipiza, Faragus. Larvae aphidopha- 

 gous. 



Mallota, Spilomyia, Xylota, Brachypalpus, Focota, Myiolepta, Chryso- 

 toxum, etc. Larvae in decaying wood or trees ; some of them (Mallota) 

 long, "rat- tailed." 



Chilosia. Larvae living in the stems of Cardium, Sonchus, Schrophu- 

 laria, Matricaria, and in fungi {Boletus edulis, etc.). 



Flatychirus, Rhingia, Eristalis, Syritia, Orthoneura. Larvae in decay- 

 ing vegetable matter, manure, or in soft mud impregnated with decaying 

 vegetable matter. 



Brachyopa, Xylota, Ghrysochlamys, Ceria. Larvae found living in flow- 

 ing sap of trees. 



Crioprora. Bred by Osten Sacken, from larvae found under oak bark. 



Microdon. Larvae common in ants' nests. The larvae and pupae of 

 this genus are very curious creatures, resembling some land-shells so 

 much that twice they have been described and named as species of 

 mollusks. 



