33 
blood-sucking Diptera, may easily be captured or killed. Owing to 
the size of the Tabanidae, the wound inflicted by the mouth-parts of 
many of the species is especially severe. Anyone who has seen 
Tabanus bovinus (Plate 19) attacking horses must have noticed the 
large drops of blood that exude and trickle from the spots bitten by 
the flies. Among domestic animals, however, horses and cattle are 
not the only victims, for in other countries mules, camels, and 
elephants suffer severely. Wild animals are similarly tormented ; 
thus in 'The Nile Tributaries of Abyssinia ' (London: Macmillan 
& Co., 1867), p. 210, the late Sir Samuel Baker, writing of the country 
between the Settite and the Atbara Rivers, mentions herds of game as 
retreating from the south before the attacks of the " Seroot," under 
which name several species of Tabanus and Pangonia arc known to 
Europeans on the Blue and White Niles. As regards the attacks of 
horse-flies upon human beings, abundant though certain species such 
as those of Hccmatopota occasionally are in the British Islands, we 
have to turn to continental records in order to understand how serious 
a pest these flies may become owing to their extraordinary blood- 
thirstiness. Thus, according to Portschinsky (' Die Bremsen (Tabanidae) 
und die einfachste Methode dieselben auszurotten.' [In Russian.] Pub- 
lished by the Ministry of Agriculture and State Domains : St. Peters- 
burg, 1899, pp. 19. — Summary in German by N. Von Adelung, 'Zoolo- 
gisches Centralblatt,' VII. Jahrg. (1900), pp. 807-808), in the Gdov 
District of the St. Petersburg Government, in Russia, horse-flies in 
summer are so excessively numerous and bloodthirsty that agricultural 
operations have to be carried out by night ; while in parts of Siberia, such 
as the shores of the River Om, settlers have been compelled entirely to 
abandon the zone infested by these flies. Noticing that horse-flies 
frequently seek pools in order to drink, Portschinsky hit upon the expe- 
dient of covering with a thin layer of petroleum the surface of the water 
in certain lakes and pools in districts infested by the flies. The result 
was a brilliant success, and the insects were destroyed in enormous 
numbers, the majority on attempting to drink adhering to the layer 
of oil, while others although they managed to fly away, were 
subsequently choked or poisoned by the petroleum. In this way 
certain localities, such as the Park of Pawlowsk near St. Petersburg, 
were completely cleared of these troublesome Diptera. It is interesting 
C 
