68 



15. BIONOMirs OF ANOPHELES T,ARV^. 



We made the following observations: 



(1) Eggs. — These are hoai-shaped, like those of Anophdes observed in India. Xhey 

 appear to be laid singly on water, but cohere by their ends, forming typical triangu- 

 lar patterns, and also adhere to floating objects, the sides of the vessel, etc. We 

 observed no facts indicating that they are ever laid on solid surfaces. In mlro they 

 take about twenty-four hours to hatch, but the period is probalily much shorter in 

 puddles. 



■ (2) Duration of larval stage. — This depends on temperature and amoimt of food. 

 Under natural conditions it may probably be only three or four days, l)ut under unfa- 

 vorable conditions (cold, overcrowding, absence of food) it may certainly extend to 

 weeks.^ There are reasons for thinking that development is much hastened by 

 bright weather, in order to enable the imago to hatch oiit l)efore desiccation of the 

 containing puddle. 



(3) Foorl. — The larvfe were frequently watched floating on the surface and feeding 

 on filaments of waterweed, amongst which they often entangle themselves. On dis- 

 section the intestine was found crammed with these filaments. It was observed that 

 in vitro the larvse scarcely grow in size unless they are given large quantities of water- 

 weed, which they dispose of very rapidly. On the other hand, larvfe were often 

 caught in puddles in which no green A-egetation could be seen. They may eat other 

 food, but it would seem as if waterweeds constitute their favorite diet. It was also 

 noted that they obtain shelter among these weeds from the current running through 

 the pools during or after rain. 



(4) Enemies. — No observations could be made vnider this head, but we often found 

 many frogs and tadpoles in the breeding pools, apparently living at peace with the 

 larvae. 



(5) Effects of desiccation. — During most of our stay in Freetown heavy showers fell 

 several times a day, so that the larvje could live secure from desiccation in all but 

 the most evanescent puddles. In September, however, there was a complete break 

 in the rains, lasting three days. A large number of the pools, even many of those 

 containing waterweed, and those fed by springs during rain, dried up completely. 

 The question whether the larva^ had the power of living in the mud at the bottom of 

 the pools could now be tested by direct observation. The break in the rains was 

 followed by heavy showers, which immediately refilled all the jjuddles. Had the 

 larvpe continued to exist in the mud, they would now have emerged again. As 

 regards the jjuddles in which the mud had completely dried, this was not the case. 

 No larvse at all were found in them for at least two days after the rain had refilled 

 them. After that interval larvae again appeared, but they were very small ones, 

 evidently just hatched from the egg. On the other hand, it was frequently 

 observed that if the mud did not become completely dry, the larva^ would emerge 

 into active existence after another shower. These observations were supported by 

 some experiments in vitro, and we therefore conclude that the larva- (;an withstand 

 partial, though not complete, desiccation.^ 



(6) The same puddles constanthi occupied. — We have suggested (paragraph 13) that 

 the iwsition of the breeding pools may change according to the seasons, but while we 

 were in Freetown there was no change of season, and we generall)' found Anopheles 

 larva? in the same puddle, namely, in those which were suitable for them. Thus, of 

 two puddles lying close togethei', one would never contain larva? and the other 

 would always contain them. The explanation of this jirobably is that the larva- 



' One of us kept i'ulex larva- alive for two months in a bottle in the cold weathei- in 

 India. 



■■'One of us reared adults from full-grown larva? kept on damp blotting paper (in 

 India), but found that the young larvae died when kept under these conditions. 



