7o 
INSECTS. 
greenish yellow colour, and of an oily consistence. All the muscles are flabby, 
and the heart is often so soft that the fingers may be made to meet through it. 
The lungs and liver partake of the disease. The stomach and bowels are pale 
and empty, and the gall-bladder is distended with bile. These symptoms seem 
to indicate poison in the blood, the germ of which enters when the proboscis is 
inserted. The mule, ass, and goat enjoy the same immunity from the tsetse as 
man and the game. Many large tribes on the Zambesi can keep no domestic 
animals except the goat, in consequence of the scourge existing in their country. 
Our children were frequently bitten, yet suffered no harm; and we saw around 
us numbers of zebras, buffaloes, pigs, palas, and other antelopes feeding quietly 
in the very habitat of the fly. There is not so much difference in the natures 
of the horse and zebra, the buffalo and ox, the sheep and the antelope, as to 
afford any satisfactoiy explanation of the phenomenon.” With the gradual spread of 
civilisation, it might be supposed that the ravages of this pest would become lessened, 
but this does not appear by any means to be -the case. Writing in 1881, Mr. 
Selous remarks that “ nowhere does this virulent insect exist in such numbers as to 
the westward of the Victoria Falls, along the southern bank of the Zambesi and 
Chobi. It is usually found in great numbers near the rivers, becoming scarcer 
and scarcer as one advances inland, till at a distance of a few miles it disappears, 
except in some particular patches of forest. Along the water’s edge they are an 
incredible pest, attacking one in a perfect swarm, from daylight till sunset; and 
without a buffalo or giraffe tail to swish him off, life would be unendurable. . . . 
About one in every ten bites (that perhaps touches a nerve) closely resembles the 
sting of a wasp or bee, as it will cause one, when seated to spring up as if pricked 
with a needle. ... I think that this plague of the tsetse flies along the Chobi 
and Zambesi is due to the enormous numbers of buffaloes that frequent their 
banks, as they always seem very partial to these animals. The bite of this 
remarkable insect, as is well known, though fatal to all kinds of domestic 
animals, is innocuous to every species of game and to man. A general belief 
exists that among domestic animals, the donkey, dog, and goat are exceptions 
to this rule ; but this is a mistake, for I have seen all three die from the effect 
of its bites.” The genus to which the common tsetse belongs is represented in 
South Africa by several species, all of which seem to be similar in habits. It 
ranges from Somaliland in the east and the Congo in the west, southwards as far 
as the Limpopo. Fortunately it is not universally distributed throughout the 
country, being somewhat local in its distribution, and inhabiting definite tracts of 
land, corresponding with the beds of rivers, from which it does not appear to spread 
to any great distance. 
Another group of flies constitutes the subfamily Tachinince, of which the 
best known examples are the spiny-flies ( Tachina ), so called on account of the 
thickness of the bristles with which their bodies are clothed. Of stout and robust 
build, these flies present a great resemblance to blow-flies and their allies, but have 
the bristles of the antennae naked, or feathery only at the base, and the scales cover¬ 
ing the balancers of larger size. The larvae, like those of the Conopidce, live 
parasitically upon other insects, such as beetles, grasshoppers, and caterpillars. 
The great spiny-fly (Echinomyia grossa), rather a local species, is the largest 
