CO885-24 — Page 380

PUBLIC RECORD OFFICE

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C.O. 885

24 PUBLIC RECORD OFFICE, LONDON

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B.-Shelter as Protection to the Adult Flies,

40. What good breeding grounds are to the young, good "shelter" appears to be to the adult-adequate protection against animate and inanimate destructive agents alike. Some confusion arose at first owing to the apparent necessity for two kinds, in conjunction or juxtaposition. Flies could always be found most commonly, during hours when they were most active, in localities where clumps of rank herbage It is in the shelter or low bush formed the predominating type of vegetation.

But invariably, unless in supplied by such that puparia are most easily found. addition shelter of a sort supplied by forest, thick bush, or large shrubs in masses is near at hand, fly has been absent or very rare, irrespective of abundance of food or excellence of breeding grounds. The explanation now accepted is that the adult fly really requires only one type of shelter, the latter mentioned, and that this is different from the type which is usually found in breeding grounds, and which suffices for the protection of the puparia as well as for the adults during their hours of activity. Active flies naturally haunt the breeding grounds (especially since their hosts are likely to be found there), but quiescent flies (including both sexes at night and during dull weather and females at some other times) must have the other sort of shelter as well. This is not easily proved, and positive proof is lacking. It is not even known where the flies secrete themselves at night and at other time when inactive, still less by what animate and inanimate foes they are likely to be assailed at such times; but it is certain that "good shelter" means the large trees in the forest as well as its undergrowth, or the low bush along the water's edge. Both, in fact, are required, and if either is absent the species is unable to exist. DISTRIBUTION AS DETERMINED BY THAT OF FAVOURED HOSTS AND BY THE LOCATION OF WATER.

41. It is said that on the mainland in Uganda Glossina palpalis is rarely On many of encountered more than two or three miles from lake or open stream. the islands only stragglers are encountered more than a few hundred yards from the shore, and this was the general rule as long as investigations were principally con- fined to those upon which only amphibious hosts occurred. But later it was found to be an invariable rule that infestation extended inland just as far as shelter was good Thus, on Bugalla, the and acceptable hosts common, and never much farther. largest island in Sesse, where antelope is abnormally numerous and well distri- buted, the highest, driest, and rockiest hills, and those two miles (the maximum distance) from the water, were found infested to a degree which represents the average for the shore of the islands as a whole (though not nearly as densely as the shore of this one in particular). Similarly, several smaller islands where varanus is common on the hills as well as on the shore (on account of distribution of forest So, too, is the large island of and open spaces) are generally infested throughout. Bukassa, which is overrun by pigs, not of wild stock, but of domestic stock run wild. 42. It is not known if the distribution would be similarly affected by man, were he to displace the antelope* and reoccupy the once populous plateaux, but it It might on account of is doubtful if this would happen on his account alone.f cattle, much as has happened on Bukassa on account of pigs, but it is believed that the fly would desert any region if supplied with no hosts more acceptable than man, sheep or goats; certainly it would do so unless man were more phlegmatic under attack than the average native amongst the writer's porters and "fly boys."

43. The effect of open water is thus shown to be in many cases, indirect. It Further study convinced that affects the hosts directly, and through them the fly.

• On the mainland the marsh buck is said not to live beyond the protection of dense forest and swamp, and is accounted a rare animal. On the islands where it has no predatory enemies, its increase has been unrestricted, and it has strangely modified its habits in many ways. On Bugalls, it no longer finds sufficient food in the swamps, and has climbed the highest hills, where it browses along all but precipitous slopes almost as freely as a goat might do. It has also taken freely to grazing and is not infrequently seen in open grass land in full day; once at midday. On the whole, it is more common on the hills, and particularly in the abandoned plantations than in its former habitat.

Evidence is somewhat conflicting concerning occurrences of fly in the hill village before depopu-

lation, but at the most these were very few as compared to the present.

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the influence of water is similarly indirect at all times. By far the best and most extensive breeding grounds are found in the old beaches, generally only a few feet above the present lake level, and, except on small islands, the writer has been unable to find a single colony of fly which was certainly independent of the protection which these provide its young. At some few points, on large islands, seemingly indepen- lent colonies were found at a distance from any beach, but there is room for doubt if these colonies were really independent of immigration. Moreover, some of these possibly independent colonies were located on the hills, at a distance from water as great as that which separated others near the shore from populous breeding places, so that location of water does not count as a factor.

44. It is not that other types of breeding ground than provided by the beaches are not attractive to the females and safe depôts for their young, but that they seem to be rarely sufficiently extensive in proportion to the area over which flies will disperse from them. In natural consequence distribution is limited to the vicinity of the shore and as far back from it as a single generation of wander- ing flies and the smaller number of their progeny reared under adverse surround- ngs will penetrate. Dispersion, whether inland or along shore, depends upon shelter and distribution of hosts. Shelter is generally good and hosts common along the shore, so that at nearly all times the fly disperses laterally, from breeding grounds located at wide intervals along shore, more freely than it spreads inland even under such exceptional conditions as are supplied by Bugalla.*

Its

45. Dispersion inland, at points on the mainland shore nearest to the islands, is not known to be as extensive as on Bugalla, and the writer has been very curious as to the reason. It was thought that either shelter or hosts would certainly be found lacking. Some three weeks have now been spent upon the depopulated penin- sulas to the eastward of Entebbe which, other than faunistically, closely resemble islands. Marsh buck is very rare upon these, but bush buck very common. habits under this, its normal faunistic environment, are very similar to those of the marsh buck under the abnormal environment of Bugalla. It is also nearly or quite None the less it cannot be shown to have any similar effect dis-

upon tribution of fly, which is limited to a narrow belt along the shore, as on most islands where only amphibious hosts are common. Reluctantly it was concluded, on these grounds alone, that the bush buck, as a host, is not as acceptable under mainland conditions as the, marsh buck under insular conditions.

as common.

The

46. Four were shot under such circumstances that a following swarm might have been expected. Not as many Glossina (one) or large Tabanids (two) were found on these individuals. No Tabanids larger than Glossina have been noted on any marsh buck shot on the islands. The circumstances in connexion with observa- tions upon the behaviour of fly toward cattle gave rise to much speculation, and little else. Perhaps the (apparent) absence from the islands of Tabanids feeding on Bovida may explain, in part, the attractiveness of marsh buck as a host. ily showed no tendency to collect in following swarms on cattle; but Tabanids were nearly always present. Perhaps in their absence such swarms would have gathered It may be that only hosts upon which the fly called in following swarms affect its distribution. It may be that none of the Bovida do affect its distribution if Tabanids are common, but that many of them may if Tabanids are rare or absent. 47. Much that would be interesting from a technical, and something that might be valuable from a practical, point of view, could be learned by a study of Glossina in relation to the various large mammals upon which it doubtless feeds to some extent, but it is doubtful if the information would be sufficiently valuable to justify the labour, which would be great. It is necessary to learn the habits of the animals themselves, and to stalk and hunt them in the particular retreats where they are safest from pursuit. The writer has had innumerable opportunities to stalk marsh burk in their sunning spots, and has succeeded only once, for they are always surrounded by thick undergrowth which cannot be penetrated without giving warning. The corresponding retreats of bush buck are even better protected, and it is characteristic of both marsh buck and bush buck to slip very quietly away, if approached under such circumstances, taking (in the case of marsh buck) the swarm of flies with them.

* Small streams flowing down from the hills have no effect on dispersion farther than that they are always bordered by bush or forest. They are present on several islands where dispersion does not extend inland, and absent on others where it does.