G. V. Hudson. — On Eristalis tenax and Musca vomitoria. 187 



Abt. XXI. — Eristalis tenax and Musca vomitoria in Neiv 



Zealand. 



By G. V. Hudson, F.E.S. 



[Read before the Wellington Philosopldcal Society, 2nd October, 1889.] 



1. Eristalis tenax. 

 Early last spring (1888) I observed a large dipterous insect in 

 the Botanical Gardens here, which I had not seen before in 

 Nev^ Zealand, but soon recognised it as the common drone-fly 

 of England {E. tenax). This species is especially interesting 

 as it exhibits such a close superficial resemblance to the hive- 

 bee {Ajns mellifica) that any one but an entomologist would 

 experience considerable difficulty in separating the two insects, 

 although, of course, structurally they are totally different, be- 

 longing as they do to two entirely distinct orders of Insecta, 

 the Diptera and the Hymenoptera. 



The resemblance in this case is, in fact, a very perfect- 

 instance of " mimicry," the harmless dipteron having assumed 

 the external appearance of the formidable hymenopteron, and 

 thus become shielded from many enemies. That this acquired 

 resemblance has effectually aided the insect in its past career 

 can be immediately seen from its great abundance, and almost 

 universal distribution throughout the world. 



The favourable influence of civilisation on this insect must 

 not, however, be overlooked, as the formation of ditches, cess- 

 pits, &c., incidental to the arrival of man has afforded its 

 larvae numerous breeding -places which formerly did not 

 exist, whilst the propagation of the hive-bee has also nO' 

 doubt indirectly assisted in increasing its numbers by main- 

 taining that dread among the insectivorous animals which the 

 appearance of a bee is usually sufficient to inspire, and thus 

 to a large extent preserving it from being eaten or otherwise 

 destroyed. 



During last April I counted upwards of thirty drone-flies on 

 a small patch of marigolds, and noticed large numbers on the 

 hills between Karori and Wadestown, so that it is evidently in- 

 creasing here quite as rapidly as elsewhere. It will conse- 

 quently be interesting in the future to observe the influence 

 that Eristalis tenax exerts on its aboriginal relatives, such as 

 E. cingulatus, Helopliilus trilineatus, incptus, &c., as, judging 

 from the behaviour of other northern importations, it should 

 largely supersede them, especially when we consider how 

 efficiently it is protected by its resemblance to a common 

 and powerfully-armed insect. The ultimate extinction of the 

 indigenous species of Eristalis and Helophilns by this mimetic 

 species would consequently seem not improbable. 



