BRITISH 



BLOOD-SUCKING FLIES. 



IN the shape of the common house-fl_\', or the bhie-bottle, Flies 

 are familiar to ever_\-one, and a brief examination of either of 

 these household pests will re\eal two of the chief characteristics of 

 the Order (DipteRA) to which they belong, — the possession of but 

 a single pair of tvings, and, immediately behind these, the presence of 

 a pair of little knobbed organs, the lialteres or balancers, which 

 represent the second pair of wings possessed by other insects. These 

 two features, — the single pair of wings and the halteres, both of which 

 can clearly be seen in the majorit}- of the plates illustrating the 

 present work, — serve to distinguish all ordinary Diptera from all other 

 insects. The winged males of Coccidre (Scale-insects), which belong 

 to the Order Rh\-nchota, though they have only one pair of wings, 

 and might perhaps be mistaken for gall-midges (Diptera), are 

 distinguished by the possession of a pair of long caudal filaments at 

 the tip of the abdomen, and by being without halteres. In a small 

 number of aberrant Diptera, as in the sheep " tick " (Plate 34), the 

 wings, or both wings and halteres, are entirely wanting, but in these 

 cases the other details of the insect's external anatomy disclose its 

 systematic position. Under the term " Flies " we include then, not 

 only the horse-flies (Tabanidje) and many other families, the species 

 of which more or less resemble the house-fly in shape, but also the 

 midges and mosquitoes, which, though very dissimilar from the 

 former in appearance, nevertheless possess all the essential structural 

 characters of Diptera. 



Excluding the Fleas (Pulicid.t), which it is better to regard as 

 forming a separate Order of insects, 59 families are recognised in 

 Verrall's 'List of British Diptera,' 2nd Edition, (Cambridge, 1901). 

 Of these, if we leave out of the question the highl)- specialised and 



