BRITISH BLOOD-SUCKING FLIES
sex mav pass the period of adult life without taking blood at all." Hine had
often seen both sexes on foliage, and observed the insects sipping up dew on
the leaves. He had also noticed, in a number of species of Chrysops and
Tabatnis, both sexes feeding upon the honeydew produced by Aphididae.
The species of Haematopota and the smaller species of Tabanus are remarkable
for the quietness with which they alight on their victims, the sharp prick
of the bite being often the first intimation of their presence. On the other
hand, the larger species of Tabanus betray their approach by their deep hum.
\\'hen once the operation of sucking blood has begun, Horse-flies, like any
other blood-sucking Diptera, may easily be killed or captured. Owing to the
size of the Tabanidae the wound inflicted by the mouthparts of many of the
species is especially severe. Anyone who has seen Tabanus verralli (pi. 29),
or T. sudeticiis (pi. 30) attacking horses must have noticed the large drops of
blood which exude and trickle from the spots bitten by the flies. Among
domestic animals, however, horses are not the only victims ; pigs and sheep
are often attacked, and in other countries mules, camels and elephants suffer
severely. AVild animals are similarly tormented. In the course of an
article on red deer in the Scottish Highlands, published in The Times of
September nth, 1926, the anonymous author remarks : " Perhaps because of
the absence of rain, the large cleg fly [probably Tabajius disti7tguendT<,s \'errall,
pi. 26] has not been seen so much this year as usual. This biting fly is at
its worst in the early days of July, and stags and hinds have to move up to
the high tops to escape it." This statement brings to mind a much earlier one
relating to the Sudan. Sir Samuel Baker (1867, p. 210), writing of the country
between the Settite and Atbara Rivers, mentions herds of game retreating from
the south before the attacks of the " Seroot," under which name several species
of Tabanus and Pangonius are known to Europeans on the Blue and White
Xiles.
Cameron (1926, p. 5) estimates that an animal grazing in an area heavily
infested with the Canadian Horse-fly Tabanus septentrionalis Loew (a species
very similar in size and general appearance to the British T. bromius L., pi. 33),
might lose as much as 100 c.c. ( i pint) of blood during the course of a hot
summer's day. The effect of such a continued drain on the vitality of stock,
coupled with the restlessness induced by the persistent attacks, can well be
imagined.
Abundant though certain species such as the commoner forms of Haematoi)
ota sometimes are in the British Isles, we have to turn to Continental records
in order to realise how serious a pest these flies may become, owing to their
extraordinary bloodthirstiness. Thus in some parts of Russia (see Portschinsky,
1900, p. 807) Horse-flies in summer were so excessively numerous and
bloodthirsty that agricultural operations had to be carried out at night, while
in parts of Siberia such as the shores of the River Orm, settlers were compelled
to abandon the zone infested with these pests. In this connection some
obser\-ations by Alajor A. D. Fraser (1920), made in North Russia during the
summer of 1919, while serving with the Vologda Force, are of such interest
as to be worth quoting in full. The observations in question were made " in
BRACHYCERA—TABANIDAE 71
the vicinity of Obozerskaya, a small village on the Archangel-Vologda railway,
roughly 80 miles due south of Archangel . "
After describing the nature of the country, and stating that the entire
district is " one continuous forest of pines, firs, etc." containing but little
undergrowth, but swampy and " waterlogged even in July, when the heat
was quite trying," Major Fraser continues : " Before I arrived in the country
mosquitoes were numerous and troublesome, and the troops had been provided
with mosquito-nets and veils. Midges were also annoying, but no
other biting-flies were in evidence until June 20th, a warm sunny day following
a couple of days of rain, when numbers of Tabanidae appeared. A day or
two later they had increased to such an extent that they were present everywhere
in swarms, and although at their worst in the forest, they were a pest
in the villages, houses, trains, etc. Near the edge of the forest many more
than a hundred Tabanidae could be counted on one person at the same time,
while hundreds of others would be flying around. In the forest itself they
were present in almost incredible numbers. There were many officers and
men in the Force who had lived and travelled in all parts of the world, but
all those I met agreed that never before had they encountered these flies in
such swarms.
" Soon after the middle of July the flies diminished very considerably in
numbers, and during the early part of Augus t only an occasional fly or two would
be seen on a particularly fine day.
" The flies seemed quite as eager to attack human beings as animals, and
at their worst were a far worse pest than ever I have found tse-tse flies. The
majority settled on one's legs, and in the forest they attacked in such numbers
that work in it was rendered almost impossible. . . . The local inhabitants
performed most of their outdoor work during the night, and kept their cattle
and other animals in their sheds during the heat of the day. When a journey
had to be made in the daytime the drivers of the horses as far as possible
selected a time when they expected a wind would rise and cause the flies to
become less troublesome. Before setting out they would rub their ponies
with paraffin, a supply of which they would take with them. They would
then proceed in convoys and make the journey as quickly as possible, using
branches of trees to beat away the flies. The leading horse in a convoy seems
to be attacked more severely than the others, and the animal's head appears
to be the favourite place of attack ; but if blood has been made to ooze from
any part of the animal, this point always attracts a swarm of flies. As for
human beings, I have heard it stated by British officers that they have been
bitten through Bedford-cord riding breeches . . . some individuals suffered
from bites which developed into nasty septic sores requiring medical attention.
" It was noticed that a small, dark-coloured fly (probably a non-biting
Muscid) constantly accompanied the Tabanidae, and sucked up any blood
which flowed from the wounds caused by them."
Goife (1931, p. 46) notes that when attacking human beings. Horse-flies
differ in the parts of the body they select. " Species of Tabanus and
Atylotus \Ochrops'\ seem to prefer the legs, either just above or just below the