Vegetation is the most important factor in determining the suitability or otherwise of an area for tsetse-flies. In all cases Glossina pallidipes occurs in what is known throughout South Africa as “bush-veld,” and, as a rule, “bush-veld” is only to be found at comparatively low altitudes (Plates xxxii, xxxiii). In Zululand it occurs from a few feet above sea-level, e.g., west shore of False Bay, to approximately 1,500 ft., e.g., eastern slopes of Ubombo Range. Glossina then may be expected to exist anywhere in the hundreds of square miles covered by trees which vary from stunted “munga” (Acacia natalitia) to the tall “umhlosinga” (Acacia xanthophloea). In some places the trees have bare trunks, e.g., “mxama” (Schotia brachypetala) and “mgano” (Sclerocarya caffra), especially where the soil is sandy. Glades up to several acres in extent may also be seen. Along the banks of rivers and in the valleys, however, the bush is generally thick, there being much undergrowth, with a canopy, overhead consisting very often of “mtomboti” (Spirostachys africana) and “mkaya” (Acacia welwitschii). There are also dotted about thickets comprising several species of Celastrus and Acacia, but a common formation is that of “mqawe” (Acacia benthami), which is dense and at times impenetrable. The dominant grass in the areas that are fairly well timbered is “ubabe” (Panicum maximum), while in the more open areas “insinde” (Anthistiria imberbis) is by far the commonest grass. In Ingwavuma, Ubombo and Hlabisa (eastern) Divisions the “fly” country is level or rather undulating; while in Mahlabatini and Lower Umfolosi Magistracies it is, on the whole, very broken, there being a constant succession of stony, sparsely bushed ridges and deep tortuous wooded ravines.