PREFACE TO THE FIRST SERIES 



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 may be killed in a 

 laurel bottle, care being taken that the leaves do not become mildewed, 

 which would probably ruin the specimens; a circular piece of white 

 blotting paper should be placed over the leaves, and frequently renewed. 

 Flies should remain in the bottle till they are thoroughly relaxed, 

 which will require a day or two; if left too long they become rotten 



