PREFACE 



THE study of Diptera (two-winged flies) is rendered peculiarly 

 difficult by the lack of elementary treatises on the subject. 

 Certain groups are fully treated in the two large (and costly) volumes 

 published by the late Mr Verrall, there are a few scattered papers in 

 various magazines, and one or two monographs (such as Lowne's on 

 the Blowfly) ; but there is nothing to compare with the numerous 

 manuals dealing with Lepidoptera and Coleoptera, to name two 

 orders only. This little book does not claim to fill the gap, but 

 it is hoped that it may be of some use to the beginner, and attract 

 attention to an order which possesses great interest, and is moreover 

 of much economic importance. It is chiefly a picture book, as pictures 

 appeal more to the eye than many pages of letterpress ; and an 

 important dipterous character — the venation of the wings — can be 

 rendered with fidelity in a photograph. 



I have found it difficult to obtain specimens set sufficiently flat for 

 photographic reproduction ; since, in photographing on the enlarged 

 scale required, no amount of "stopping down " will produce an image 

 sharp all over, unless the subject be fairly in one plane : in addition 

 to this, some species when set and dried shrivel up, and give but a 

 poor idea of their appearance when fresh. This of course chiefly 

 applies to the bodies of flies, the wings and legs are not so affected. 



Flies may be taken with the usual entomological net, preferably a 

 green one, as less likely to cause alarm than a white one. Mosquito 

 netting, which may be dyed the required colour, is much better than 

 green leno. The net should be fairly large, but light and easily 

 managed, as many flies are very swift and strong on the wing. When 

 caught, the fly may be transferred to a glass bottomed entomological 

 box : a good supply should be carried, and it is better that only one 

 specimen be placed in a box. On returning home the flies niaj- be 

 killed in a laurel bottle, care being taken that the leaves do not 



