SOME OTHER FLIES 21 



a number of other very common flies of a generally 

 similar full-bodied shape, in most of which colour 

 stripes and bands more or less suggest a comparison 

 with wasps. The numerous species native to Great 

 Britain are widely distributed, and, excepting the rare 

 and very hairy Merodon narcissi, of which the larvae 

 feed on liliaceous bulbs, none is injurious and some 

 are beneficial. Nearly all the flies of this family 

 frequent flowers. The habit of many to hover for 

 hours about a favoured spot, as if for mere pleasure, is 

 remarkable; but it is not generally recognised that 

 some of these hover-flies (of the genus Syrphus) are 

 hawking for winged aphides and other small insects, 

 which they quickly suck dry and drop whilst still on 

 the wing. Many of the flower-frequenting Syrpkidce 

 are great devourers of pollen ; all have strongly 

 developed suctorial mouth parts. 



The larvae of the various syrphid flies differ greatly 

 in appearance and habit; some are terrestrial; some 

 aquatic ; some semi-aquatic ; some feed on decadent 

 vegetation; some on sewage and filth, and some are 

 insectivorous. Most useful to the horticulturist are 

 those of the genus Syrphus, which feed on green-fly 

 and other aphides. The most curious in shape are the 

 " rat-tail " maggots of the common drone-fly, Eristalis 

 tenax (also others of allied genera), which can extend 

 their long tubular tails and breathe atmospheric air 

 through the same whilst lying under water. The larvae 

 of the genus Volucella are found dwelling in the 

 nests of bumble-bees and wasps ; it is rather uncertain 

 how far they are commensal, or parasitic, or devourers 

 of dead matter. Some of the syrphid flies are single- 



