REPORT OF THE MALARIA EXPEDITION. 
23 
meal of blood. As Anopheles larvas were not found in vessels of water close to houses, tlie only 
inference wliich remains seems to be that the pregnant females must return, not to any water, but 
to some pool suitable for lier offspring. If such a pool exists close to the house where she obtained 
her meal of blood, her journe\' need only be a short one ; but if it be at a distance, she must fly 
correspondingly far— and ma\' often be obliged to do so against the wind, or through heavy rain, 
or between trees. 
It is therefore highh' probable that, unless they can find animals and birds to feed on, 
Anopheles must seek tlieir food in houses which are as near as possible to their breeding-pools, and 
also, vice versa, select pools for their eggs which are as near as possible to the places wlierc thev 
obtain their food. In other words, the\' are not likely to neglect adjacent houses and pools in 
order to visit more distant ones. ()t course man\' individuals must go astray- must be carried 
away by winds and so on ; but it seems reasonable to expect that, as a rule, the breeding-pools and 
feeding-grounds will be as close together as possible. 
Where necessity compels, however, it is probable that Anopheles do travel considerable 
distances to and fro. This must cspecialh be the case diu'ing the dr\ season, when the pools must 
be much more rare -unless we can show that at that time tiie surviving adults cease to feed at all 
and " hibernate." 
It is noteworthy that in the Tower Hill barracks we nev er found Anopheles, although there 
were numerous breeding-pools at a distance of only 500 yards, both to leeward and windward. 
The barracks are situate on a hill onh- 400 feet above the sea, and are surrounded by open grass, 
over which the insects could fly or be carried by the wind ; though it should be added that 
occupied houses intervene between the pools and the barracks. Perhaps the insects are all 
attracted by these houses. The same thing was observed regarding the barracks on Mount 
Aureole. 
The question as to the maximum distance possible between a house and a breeding-pool 
IS an important one, but difficult to reply to. The distance will probably depend largely on local 
conditions, prevalent winds, screens of trees, presence of other animals, etc. We must remember 
that while wind may assist the insects going one wa\', it ma\' equally oppose their return. On 
the whole it appears difficult to imagine that this maximum distance can be very great — more 
than half a mile, for instance ; and certainh- we never found Anopheles larvs* except in mucii 
closer proximity to houses. 
Certainly gnats can \'isit ships lying fairly close to the shore. Dr. Wigglesworth was kind 
enough to give us some gnats which he had caught on board the S.S. Fantee, on the West Coast 
of Africa ; and one of these was an Anopheles. But it must be remembered that insects blown 
across water are likely to tra\ el much further than on shore where hills, trees, and houses 
intervene to afford them rest and shelter. 
If large numbers of Anopheles are found really far from human habitations, it will be not 
unreasonable to suppose that they can procure other besides human food. Anopheles are known to 
feed on horses and cattle, and may possibly bite other mammals, birds, and even reptiles. But it 
must be remembered that, in towns and villages at least, men are generally the commonest 
vertebrates present. 
