196    THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ I, III

    As a rule, Tabanids attack animals standing in the sun, as we have frequently
observed while collecting these flies in various localities in India. Writing of the
Tabanids of Pusa, Isaac [1925] states that Tabanus macer is generally active from
mid-day to evening, attacking animals standing in the sun, whilst T. rubidus is
active when the day is bright and warm. On the other hand, T. tenens, which is
the most abundant species at Pusa, was found by him to be most active at sunset
just before dark, when the females came in large numbers to cattle. It would be
interesting to recall here the experience of workers in this respect in certain other
countries. Williston [1908] working in U. S. A., observed that none of the Tabanids
was active on dark, cloudy days, though some were partial to shady woods, but
they were most plentiful about cattle and horses while the sun was shining. On
the other hand, Lutz [1923], in Brazil (where he records a total of about 300
species), states that Tabanids are more frequent in the shade in forests or when the
sun is low and that some species are even crepuscular in habits. In India some
species occasionally come in to light at night and it is probable that some Tabanids
are normally nocturnal.

    Several members of this family have been shewn to be capable of transmitting
Surra mechanically. Of these mention may be made of Tabanus striatus in the
Philippines (Mitzmain), T. striatus and T. rubidus, especially the latter, in Java
(Nieschulz), and of T. rubidus, T. nemocallosus in India (Cross, Patel, Kahan Singh,
Abdulla Khan). Of other Tabanid-borne diseases of animals, reference may be
made to Anthrax, conveyed by T. striatus (Mitzmain, Nieschulz), T. rubidus and
Chrysops flavicinctus (Nieschulz); hæmorrhagic septicæmia from buffalo to buffalo
(Nieschulz); and sarcocystis (Sergent). Under natural conditions, the existence of
a relationship between outbreaks of trypanosomiasis on the one hand and the
relative abundance of Tabanids on the other is strikingly illustrated by the following
information abstracted from the Annual Reports of the Egyptian Veterinary Service
for 1916 and 1917 (Trop. Vet. Bull., VIII, 274 ; Sept. 1920): " For a number of
years past Mason had noted that the Tabanidæ which carried trypanosomiasis, viz.,
T. taeniola and T. ditaeniatus, were usually very numerous during the fly season in
the Suez Canal Zone, along the Ismailia Canal and in Eastern Sharqûya ; this was
what happened in 1915 and a considerable number of cases of trypanosomiasis
occurred in Army Camels in consequence. During 1916 Tabanids were fortunately
not observed in the above localities although the number of camels had greatly
increased. No cases of trypanosomiasis apparently occurred in the Canal Zone
during the year.

    " For the same reason the Wadi Natrûn District remained free in 1916. On
the other hand, both the above species of Tabanids were extremely numerous as