818 Marvels of the Universe 
dealing may be described as ordinary-looking dark-brown, 
blackish or black, yellowish-brown, or yellowish flies, varying 
in length from about a quarter of an inch or rather more in 
the case of the smallest kind, to about half an inch in that of 
the largest, with in all species a prominent proboscis, or beak, 
which, when not in use, projects horizontally in front of the 
head. The position of the wings in the resting insect is a 
point of the highest importance, since, coupled with the 
prominent horizontal proboscis, it affords a ready means of 
distinguishing a Tsetse from any other blood-sucking fly 
for which it might otherwise be mistaken ; instead of diverging 
at the tips like those of a house-fly, the wings of a resting 
Tsetse-fly lie closed flat over one another down the back, like 
the blades of a pair of scissors. 
All Tsetse-flies feed on blood, and the blood-sucking habit 
is common to both sexes. Human beings, wild and domesti- 
cated animals, birds, and even reptiles, are attacked with 
apparent impartiality, and with such avidity that, if per- 
mitted to feed undisturbed, a Tsetse, in the short space of from 
twenty to forty seconds, may become “ swollen out like a balloon 
with bright red blood.’’ Tsetse-flies are sometimes met with 
literally in swarms; on other occasions, even within a fly- 
belt, few or none may be seen; they are most active on 
bright, sunny days, and may be equally blood-thirsty throughout the day or (in very hot 
weather) be specially aggressive at certain periods—before eight a.m., and again after four 
p-m., and about sunset. To some extent, no doubt, these details vary with the species, and are 
also dependent upon the locality and season ; certain kinds of Tsetse are known to bite by night 
as well as by day. 
The manner in which Tsetse-flies reproduce their kind is not the least remarkable characteristic 
of these wonderful insects. Instead of laying eggs like the majority of flies, a female Tsetse gives 
birth at intervals to a full-grown maggot, each maggot being produced singly, and, until its develop- 
ment is complete, being retained within the body of the mother, and there nourished by a special 
secretion. As a rule the maggot is deposited on loose, sandy soil, into which it promptly burrows 
and forthwith changes into a hard, dark-brown 
or black chrysalis, from which the perfect fly 
makes its escape some five weeks later. 
For nearly fifty years it was believed that 
the death of domestic animals after being 
bitten by Tsetse-flies was due to the action of 
a peculiarly powerful poison, which was sup- 
posed to be elaborated by the insect itself and 
injected into its victim while the fly was sucking 
its blood. In 1895-96, however, the popular 
theory was completely exploded by Bruce, who 
showed that Tsetse-fly disease in animals is 
caused by a microscopic living organism, which 
exists in the blood of many different kinds of 
GRUBS OF THE TSETSE-FLY. 
The maggot is not deposited by the 
mother until fully grown, and only one is 
produced at a time. Note the notched 
black hinder end characteristic of Tsetse- 
fly maggots. (Four times natural size.) 
PUPAE OF THE TSETSE-FLY. 
The second stage of a Tsetse-fly—a hard barrel-shaped 
wild animals in Africa without apparently 
doing these creatures any harm. When a 
case, from which the Fly eventually makes its escape by push- 
ing off a cap from the rounded end. (Five times natural size.) 
