110 DIPTERA. 



worms, and even small shell-fish. The family is a 

 numerous one. 



I pass over the families of Lonchopteridw , Platij- 

 pezidce, and Pipunculidce^ as the species are not in 

 any way remarkable. 



The flies of the family Syrphidce are very numerous ; 

 they feed chiefly on the nectar of flowers, over which 

 they hover hawk-like ; such is the rapidity of their 

 vibration that the wings are almost invisible ; if 

 alarmed they dart away with amazing velocity, soon 

 returning to the same place. 



One species {Syrphus pyrastri) may be often seen in 

 gardens ; it is a blackish blue with pale hairs ; on the 

 abdomen are three interrupted yellow or whitish bands. 

 The larvae of the Syrphidce are leech-like creatures in 

 form, having generally a broad posterior extremity and 

 a narrow flexible head ; they are for the most part pre- 

 daceous in their habits, feeding on the plant-lice or 

 aphides. I have often seen a Syrphus larva holding on 

 high in his mouth a mischievous little plant-louse, so 

 that these flies must be put amongst the gardeners' and 

 farmers' friends. 



The species of the genus Eristalls are remarkable for 

 the length of the tail in the larvae. The perfect insects 

 are of large size, and resemble bees both in form and 

 colour, for which they are often mistaken. Eristalls 

 tenax is, perhaps, the species most generally known. 

 The larvae or rat-tailed maggots live in stagnant water, 

 in the filthiest of mud, and in sewers ; the tail is a kind 

 of telescopic tube, and contains a double air-channel, 

 which is the respiratory organ ; when the maggot is 

 immersed in thick filthy mud the respiratory tail is ex- 



