7 o 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 satisfactory 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 clue 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 Somalilaiicl 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 



