336 C. F. M. SWYNNERTON. 



VIII. — The Food of the Fly. 

 Observations by numerous workers elsewhere have shown that tsetses living 

 in contact with large reptilian and avian populations very freely utilise the former, 

 and perhaps also the latter as food. Gut examinations even of G. morsitans have 

 shown in some cases (Lloyd) a remarkable proportion of non-mammalian contents ; 

 the same fly has been seen to feed on the bare neck-wattles of an uncon fined ground 

 hornbill (also Lloyd) ; a case is on record (Ensor) in which a fly, " almost certainly 

 tHorsitans/* was observed through glasses trying to get under a perched hawk's 

 wing ; and in the Entebbe laboratory Glossina 'palpalis " fed readily on captive 

 fowls, creeping under the wings to reach the poorly protected parts " (Bagshawe). 

 It follows from this last and extraordinarily important observation (which 

 does not surprise me when I remember that morsitans rather reminded me of Olfersia 

 in its low poise and clever sidelong movements in response to attempts to catch it) 

 that birds are not necessarily protected against tsetses by their armature of feathers, 

 though many of them certainly are by their agility and insect-eating habits. Yet 

 young birds, whether nestlings or runners both in the nest and for a time after 

 leaving it, are defenceless— and abundant just when the fly is abundant. Also 

 the fly (as met with on this trip) retires to rest later than do most diurnal birds, 

 the latter being thus relatively unprotected from it during a very brief portion 

 of each day when the fly is particularly active — ^but the bird (it must be admitted) 

 less conspicuous. 



Such facts, with the way in which birds, including ground hornbills, keep to 

 definite beats, the whole of which they work every few days, and the fact that nearly 

 the whole bird-population searches for its food and breeds either usually or very 

 commonly within a few feet of the ground, the search being conducted with much 

 bustle and conspicuousness on the part of the large combined parties of small birds, 

 must be taken into account when we attempt to explain such cases as Umzila's 

 .failure to keep cattle near the then much smaller rubber forests (in spite of a great 

 hunting population and a strenuous effort to exterminate game) and when we 

 consider the question of destroying game to starve the fly. At the same time, 

 so far as small birds are concerned, it seems to me that the fly's habit of choosing 

 harmoniously coloured surfaces to rest on suggests that its effort will be to evade 

 rather than attack them during their active hours and stages of existence. I feel 

 also that the very striking connection between the fly's breeding habits and game 

 must be given its full weight. 



My own observations dealt only with mammals. 



Mammals from the smaller Ungulates downwards. 



The natives of the morsitans area were unanimous in their statement that tsetses 

 feed freely on baboons, and that " wherever you find baboons you will also find fly." 

 They gave me many instances in which baboons driven from their gardens had 

 left numerous replete flies behind and others in which flies were attracted in numbers 

 to baboons that were killed. Simpson's similar personal observations and native 

 statements on the Gambia and Gold Coast will be recalled, as will Lamborn's 

 indirect evidence. Monkeys {Cercopithecus fygerythrus, which lives in lower bush 

 than C. albogularis beirensis and raids natives' gardens) were stated more rarely 



