T2 
extremely aberrant Nycteribida;, which, doubtless, suck blood, but, 
being exclusively parasitic on bats, are of no practical importance, the 
blood-sucking habit is met with in only eight. Included in this total 
are the Psychodidae and Leptidae ; as regards the former, the blood- 
sucking genus Phlebotomus does not occur in Great Britain, and 
although blood has been noticed (by the Rev. A. E. Eaton) in the 
abdomen of a British specimen of Sycorax silacea, Hal., the insect has 
not 3'et been observed in the act of sucking blood, so that for our 
present purpose the Psychodidae may be left out of account. The 
same course may be taken in the case of the Leptida?, for no species 
of this family has yet been recorded as sucking blood in the British 
Islands, although in France the common British Leptis scolopacea, 
Linn, (as also L. strigosa, Mg. — a " reputed " British species) has been 
observed in the act of doing so on two or three occasions. The 
number of families of British Diptera that include blood-sucking 
species is therefore reduced to six, — the Chironomidoe (midges), 
Culicidae (gnats or mosquitoes), Simulidae, Tabanidae (horse-flies), 
Muscidae, and Hippoboscida:. In two of these, the Chironomida; and 
Muscidae, the blood-sucking habit is exceptional and confined to a 
few species ; in the remainder, with the exception of a few small 
genera of Culicidae, the species of which do not suck blood, it is 
universal in the female sex, to which, with the exception of the 
Muscidae (and possibly of the Hippoboscidoe), the habit is restricted. 
It should be noted that most, if not all, mosquitoes are also capable of 
subsisting upon the juices of plants. 
The number of species of blood-sucking flies that occur in the British 
Islands cannot be stated precisely, since the total of the blood-sucking 
species of midges (genus Ceratopogon,sens.lat.)a.n& that of our indigenous 
species of Simulium is at present entirely uncertain. If, however, we 
count each of these groups as numbering a dozen species (certainly 
not an extravagant estimate), and include the two species of Nycteri- 
bidae, the number of British species of blood-sucking flies would 
amount to 74. The total number of species of Diptera recognised as 
British at the present time may be taken as between 2700 and 3000. 
With these introductory remarks we may proceed to a consideration 
of the species illustrated in the plates, which represent the principal 
British blood-sucking flies, 
