54 B R I T I S H BLOOD-SUCKING FLIES
Rumania, Bulgaria and Jugoslavia nearly 20,000 domestic animals were killed,
including horses, cattle, sheep, goats and pigs, besides wild animals, such as
deer, hares and foxes, all in the latter half of April. In 1934 the number was
even larger, partly owing to the fact that the flies spread to districts where the
peasants were unfamiliar with the pest and with the procedure necessary to
protect their beasts.
Another black-fly which has caused enormous losses of live-stock is the
" southern buffalo-gnat " {S.peamrum Riley), which in some seasons develops
FIG. 21.—Wings of Si-mulium : a, 5 . hirtipes Fries ; b, a species resembling 5. ornatum Mg.
in vast numbers in parts of the Mississippi valley. Mules appear to be particularly
susceptible to its attacks ; over a thousand of them were killed by the
flies in the year 1931. and over 500 in April 1934- It is said that neglect of
dykes during and after the civil war was one of the mam causes of black-fly
plagues during that period, through the multiplication in times of flood of small
streams suitable for breeding S.pecuarum.
The attacks of black-flies on man are fortunately less serious, and fatal
cases have been but rarely placed on record. Nevertheless these flies may be
so numerous and venomous (as, for example, in parts of northern Canada) as
to render large tracts of country more or less uninhabitable during the summer
N E M A T O C E R A — S I M U L I I D A E 55
They are also a scourge in several islands of the Marquesas group, in Northern
India and Burma, and in many parts of tropical Africa. Some species appear
to be unable to pierce the human skin, but without actually biting can make
themselves very offensive by their pestering attentions, and by getting into the
eyes, ears or nostrils.
The bite is apt to be more painful than that of a mosquito, and often results
in the development of a hard lump or swelling which may persist for days or
even weeks.
^ In recent years many discoveries have been made regarding the transmission
of parasitic worms of the genus Onchocerca by species of Simulium
Fig. 22.—Tarsi of Simulium, with claws more enlarged (but all to same scale), a. hirtipes, hind
tarsus ; b. .S. ornatum, hind tarsus ; c. latipes, front tarsus ; d. equinum, front tarsus / e ^
ornatum, front tarsus ; f. .S". morsitans, front tarsus.
Following up a suggestion made by F. W. Dry in 1922, Blacklock (1926)
demonstrated that the worm Onchocerca volvulus, which in the young stace is
a common human parasite over a large part of Tropical Africa, undergoes
development and is transmitted by Simuliujn damnosum Theobald, and
subsequent workers have shown that neavei Theobald is also a carrier of
this parasite. The worms give rise to small subcutaneous nodules or tumours
and skin eruptions, and in some districts are also a frequent cause of blindness.
A similar parasitic worm {Onchocerca caecutiens), causing similar troubles of
the skin and eyes, is common in the coffee-growing districts of Guatemala and
Mexico, and has been found by Strong and others to be carried by three species
of Sunulmm, S. ?netallicum Bellardi, 5. ochraceum Walker, and callidum.