PREDACEOUS LARV.^ 57 



and burn the barrel. It is thus that a very primitive 

 custom has now become of practical value, for we 

 encouraged these liumble folk always to keep a fish 

 in their barrel — that is, if it were necessary for them 

 to have a barrel at all. 



In Trinidad I also found in certain of the coolie 

 " ranges " on sugar plantations, that it was a common 

 practice to keep a hsli in the drinking-water barrel, 

 but they would not inform me why they did so. 



Besides fish, other enemies or auxiliaries have been 

 described. The Avater boatman, Notoncctn, has been 

 shown by Branch and Patterson of St. \^incent, amongst 

 others, to suck dry the larvae of mosquitos. Similarly, 

 it is supposed that the water spider helps also in the 

 work by continually harassing the larvae when they 

 come to the surface to breathe. A most satisfactory 

 circumstance amongst larvae is the cannibalistic ten- 

 dencies of many of them. The obserxations of Dr. 

 Urich of Trinidad and others demonstrate tliat the 

 larvce of Megarhinus triiikladensis and M. supei'bus 

 and Sabcthcs undosus are predaceous and feed upon 

 other larvas. In otlier words, there appears to be 

 a bitter struggle for existence amongst larva? when 

 they find themselves at close quarters. All these are 

 observations well worthy of further study, for it is 

 evident tliat man possesses most powerful allies in 

 the natural enemies of the mosquito which may do 

 much to help him to keep under the mosquito 

 pest. 



The common artificial culicide is kerosene oil ; a 

 small quantity is poured on the surface of the water 



