8 THE BOOK OF THE FLY 



This orck-i i^ charactered by the fact that all the 

 specie art- furnished with one pair of wings only: 

 dis = double, pteron = wing ; they all undergo a me- 

 tamorphosis analogous to that of four-winged insects. 



The dipterid flie> arc- apt to be popularly recogni-ed 

 as flies (with fat bodies) and gnats (with slim bodies) ; 

 but they may be more intelligently classified (with a few 

 anomalous exceptions) as flies (a) having a trunk-like 

 mouth or proboscis (miscalled a tongue), terminating 

 with bilobed suctorial lips, and as flies () having a 

 bayonet-like trunk, or a sheaf-like tubular spike with 

 skin-piercing lancets. No two-winged flies have stings ; 

 the tail of the female, which terminates with the 

 ovipositor and is retractile in a telescopic manner, is 

 very soft and quite unlike the sting of the ichneumon 

 or the ovipositor of the "saw-fly," both of which 

 possess two pairs of wings like bees and wasps, and 

 therefore are classified with the insect race called 

 Hymenoptera. 



Omitting Aphides (green-flies, plant-lice, and the 

 like) which are an " order" by themselves, and exclud- 

 ing gnats of slim form, mosquitoes, and midges, which 

 are mainly crepuscular, nocturnal, or shade frequenting, 

 we might try unscientifically to sub-divide the more 

 conspicuously sunshine-loving and day-flying flies 

 into: (1) flower and honey seeking flies; (2) cattle 

 pestering sweat-flies ; (3) skin-piercing, blood-sucking 

 flies ; (4) insectivorous flies ; (5) fungus flies ; (6) 

 carrion and filth flies; and to these must be added 

 another small group (7) which comprises those of the 

 wondrous family of the (Estridoe, the most horrible 

 though not the most injurious of the animal perse- 



