﻿BRITISH WEST INDIES. 257 



There seems reason to believe that, in selecting a suitable situation for deposit- 

 ing her eggs, the female Anopheles will be influenced by the presence of food and 

 shelter ; and it is possible that the emanations of decomposing vegetable matter 

 may perhaps be an attraction. 



The following experiments support these suggestions : — 



(a.) A shallow wooden vessel was placed among a number of pools which 

 contained decomposing and suspended matter, the water in the vessel being quite 

 clean and clear. The surrounding pools produced numerous larvae, but none 

 appeared in the vessel. 



(b.) Two similar tubs were exposed six yards apart ; one contained a little 

 bran and meal stirred into the water, the other had absolutely clean water. In a 

 few days numerous Stegomyia larvae appeared in the former, while far fewer 

 appeared in the latter. The bran and meal had undoubtedly attracted the gravid 

 females. 



The size of the pool is of some importance ; large sheets of water are eschewed, 

 but pools of moderate size are preferred to very small ones. Thus, in a piece of 

 well-protected ground there were two freshly formed pools about four feet square 

 and numerous small puddles about six inches to one foot across ; larvae were 

 numerous in the two larger, but were never present in the smaller pools. This is 

 one of many similar observations, and exceptions are few. 



Naturally, in dry weather, the female must find some place in which to deposit 

 her eggs, and then they are laid in a number of less favourable situations, such 

 as the edges of streams and rivers, in overgrown garden tanks and permanent 

 pools, where they have little chance of becoming imagines. Again, on other 

 occasions, a few larvae are likely to be found in these unusual situations, because 

 there has been a vast production of mosquitos in the neighbourhood, and a few 

 stray females will lay their eggs in these places. Thus, in certain marsh-land 

 in 122 searches, I have found larvae on 86 occasions, but only twice at the 

 edges of a neighbouring stream, and both occasions were after a favourable 

 period which had produced myriads in the marsh. 



The adult Anophelines have a struggle in life, though probably less severe 

 than that of the larvae ; anyhow, the struggle is less apparent, but the elements 

 and their natural enemies must destroy a large number. Being very delicate 

 insects, wind and torrential rain are very adverse to them, and, immediately after 

 rough weather, few, if any of them, can be found. They are preyed upon by 

 spiders of all kinds ; often a pool is found which contains larvae, and so great is 

 the network of spider-webs above the pool, that it is difficult to understand how 

 the emerging mosquito can escape becoming entangled. This is especially the 

 case in the more permanent pools in dry weather. Lizards, small frogs and 

 dragon-flies also undoubtedly devour a considerable number of mosquitos. 



The female Anophelines fly no further than the nearest blood-supply. This is 

 well shown by the following observations :— 



(a.) A certain village is situated in a narrow valley ; on one side is the sea 

 coast and behind it is a swamp. In the houses nearest the swamp large numbers 

 of A. albimanus are often found, but rarely can they be obtained from the 

 dwellings nearer the coast, and only 150 yards away. 



