RESEARCH IN BRITISH WEST AFRICA. 22) 
is the fact that this holds true for large launches and steamers; this was 
very marked in the Bintang Creek. When the ship was approaching the river 
bank, swarms of tsetse flew on board, but if the vessel were actually tied up, 
few if any were seen, whereas as soon as the steamer cast off, tsetse at once 
renewed their attacks. This must be borne in mind in the selection and clearing 
of any parts in a tsetse area, such as wharves, ferries, etc., where there neces- 
sarily is considerable movement. In the Gambia, for instance, at the wharves 
which are used for loading ground nuts, there is a continual stream of natives 
passing to and from the schooners or steamers. This state of affairs furnishes 
ideal conditions for attack by tsetse. 
Range of Flight.—As is well known, G. palpalis prefers to remain in the shade 
and near the ground, preferably in low scrub, and darts out into the open in the full 
sunlight only when in search of a meal. The maximum distance to which a 
tsetse will venture into an area with no shade is of great importance in delimiting 
clearings. Various estimates have been given, but although one has seen tsetse 
in camps separated from the bush by over 200 yards of clearing, it is not fair to 
assume that this distance was actually and deliberately traversed in one flight. 
It is quite possible that these isolated examples followed the natives or horses, a 
mode of procedure which they often adopt. On one occasion, however, when 
on board a launch more than 100 yards from the beach, 1 sawa G, palpalis tly on 
board in the cool of the afternoon, and in view of this and similar observations, 
150 yards may be put down as the lowest estimate for clearing, though 200 yards, 
if possible, should be aimed at. 
Effect of Sun.—G. palpalis, more than most other insects, is easily killed by 
heat, and cannot stand much exposure to the direct rays of the sun. When a 
number of insects of various kinds are transferred from a net into glass-bottomed 
boxes, prior to going to camp, it is almost invariably found that the tsetse 
are the first to succumb to the heat; in fact, if one is out for any considerable 
length of time, it is difficult to keep these flies alive without making a few 
air holes in the lid of the box and keeping it in a cool place. 
Clothing.—There is now no question but that tsetse can, and do, bite through 
cotton and woollen clothing, and those even if of a thick texture, e.g., heavy 
tweed trousers. In many cases one has noticed that these insects have a predi- 
lection for certain colours, especially black, and a good illustration of this has 
been cited on page 210. In tsetse-infested areas, the ankles should be specially 
protected. Putties or leggings worn with riding breeches are ideal, but, as was 
mentioned before, “ shorts” should not in any circumstances be worn, Khaki has 
many advantages, and of dark colours, is probably one of the least attractive to 
this species. 
Enemies.—The question of the natural enemies of the tsetse is an all-important 
one, but it is very difficult to get reliable information on the subject. During my 
tour in the Gambia, I examined the stomach-contents of a large number of birds 
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