106 SOME MINUTE ANIMAL PARASITES 



numbers are too few to make much impression on 

 the progress of " blight " on roses and beans in 

 England. Such is also true of the mosquito, but 

 the destroyer is found in the form of certain small 

 fish, known as "millions," inhabiting muddy swamps, 

 in Africa more particularly. These fish eat the 

 larvae greedily, but even in their natural haunts they 

 are unable to gain access to all the spots where the 

 mosquitoes breed, and consequently are unable to 

 completely " destroy the destroyers." Reliance on 

 fish and other animals to keep down mosquitoes is 

 only inviting disaster in most cases, or if the exter- 

 mination is attempted on a large scale there are sure 

 to be numerous escapes. 



All fish do not eat mosquito larvae. Experi- 

 mental work with fish as mosquito destroyers in 

 India showed that but few of the common species 

 available were of use in this direction. From fifty 

 to one hundred larvae were placed in tanks, and two 

 or more fish put with them. The best results were 

 obtained with young Barbus, which ate all the larvae 

 within a few ^ninutes. With the catfish and Tricho- 

 gaster the larvae slowly disappeared, while Polyacan- 

 thus and a small adult carp made no use of the 

 larvae as food. 



Nevertheless, places in West Africa are known to 

 be free from mosquitoes, and any larva seen is 

 greedily devoured by the fish in the water, and even 

 in the mud along the banks of the stream. The 

 small fish known as " millions " are also sent from 

 place to place in the neighbourhood of the Nile 

 Valley for use in mosquito destruction. 



