TSETSE-FLIES AND COLONISATION 215 



folds, climbs to the top of some of the taller trees, sending down 

 long lianes and fruiting branches, and in August its beautiful 

 pappus-bearing seed lies scattered over the land like giant 

 thistle-down. It is one of the most grotesque as well as one 

 of the most characteristic plants of the forest. In more open 

 country one finds a leguminous tree in some abundance, its 

 enormously long, pendulous fruiting pods hanging from its 

 slender branches in great profusion. Antelopes eat portions 

 of the pod, and grey hornbills and squirrels extract the small 

 beans. There is some doubt as to its botanical name, but it 

 is possibly a representative of the genus Parkia. A beautiful 

 yellow-flowering Cassia (C. goratensis) grows in similar bush- 

 like country, but is not very common. 



In such country, and amongst such surroundings, the 

 Impala antelope makes its home and the common tsetse 

 (Glossina morsitans) propagates its species. Three things 

 are therefore apparently correlative : the Sanya tree, with 

 shady undergrowth, the Impala antelope and Glossina morsi- 

 tans. In other words, " Sanya country " and " Fly country " 

 are one and the same, and such also is the favourite resort 

 of one of the commonest of the vertebrata in the Upper 

 Shire. This, however, is but a local picture of a portion of 

 the fly area in Nyasaland 1 as seen during the winter, when 

 the tropical sun pours through the almost leafless trees, 

 rendering the tenacious soil indurate and robbing it of all 

 moisture. There is practically no humus, certainly no sand, 

 and there is little else but sun-baked clay until the rains 

 commence in October, when the land becomes plastic and 

 fertile. 



The food of tsetse-flies consists entirely of the blood of 

 animals, chiefly that of the larger mammals and man, but 

 sparingly also of avian and reptilian blood. 



The natural enemies of these insects do not appear seriously 

 to check their increase ; in fact tsetse-flies seem to have struck 

 a balance in this respect. A predaceous wasp (Bembex forci- 

 pata Handl.) stores her brood cells with these and other 



1 It is well known that O. morsitans occurs in other parts of Nyasa- 

 land where Sanya trees (Copaifera mopanie) are absent. 



