170 



MOSQUITOES OF NORTH AMERICA 



these larvae prey upon the small red worms known as Tubifex or upon the larvas 

 of Chironomus. One of us (Knab) found that larvae of T any pus dyari, acci- 

 dentally introduced into breeding- jars, were very destructive to mosquito larvae. 



A remarkable ease is that of an adult fly preying upon mosquito larvas. J. 

 Mitford Atkinson gives an account of Lispa sinensis Schiner, an Anthomyid fly, 

 which at Kennedy Town, Hongkong, was seen to be eating the larvae of mosqui- 

 toes. On stirring up the stagnant water crowds of larvae were disturbed. " The 

 flies pounced down upon them and rapidly devoured larvae almost as long as 

 their own bodies ; at times they would fly away with the larvae in their mouths." 

 The flies were determined by Mr. E. E. Austen. 



Dr. Paul Osterhout, of Bocas del Toro, Panama, has recently observed flies 

 of the family Dolichopodidse, well known for their predaceous habits, to attack 

 mosquito larvae in a similar manner. We quote the following from his letter to 

 the Surgeon-General of the Public Health and Marine Hospital Service : " A 

 short time ago, in passing through the outskirts of the town, I saw a large 

 swarm of small flies seemingly very much occupied about a small pool of water 

 standing in a wagon track (the track had been undisturbed for several days 

 from the appearance), so I stooped to see what the commotion was about and I 

 saw hundreds of these small flies and thousands of mosquito larvae. I remained 

 for some time watching the commotion and saw several of the flies catch the 

 larvae and drag them to the dry earth and devour them." 



D'Emerez de Charmoy, the Director of the Museum in the Island of Mauri- 

 tius, has made a study of the natural enemies of the malarial mosquitoes in 

 Mauritius. He has drawn up the following interesting table showing at a glance 

 the results of a series of experiments which he made to determine the relative 

 effectiveness of certain species of insects and of a small fish in destroying mos- 

 quito larvae : 



Enemies. 



Number 

 of individ- 

 uals. 



Dineutes indus 



Cybister desjardinsi 



Hydaticiifs exclamationis 



Libellulid larvse 



JVepa larvfE 



Ranatra larvas 



LarvfE of Culex tigripes. 

 Cyprin dore (3V2 in. long) 



Numberof 

 larvae of 

 Anopheles 

 in this re- 

 ceptacle. 



Least 

 quantity 

 of Anoph- 

 eles larvae 

 eaten per 



hour. 



Disap- 

 pearance 

 of larva: 



after: 



Quick destruction. 

 Indifferent destruction. 

 Indifferent destruction. 

 Capture with difficulty. 



Quick destruction. 



Various adult insects have been found to prey upon adult mosquitoes. Dragon 

 flies have already been mentioned and there is no doubt that mosquitoes furnish 

 their quota of the food captured by these insects while on the wing. In this 

 connection the crepuscular habits of certain species of dragon flies should be 

 noted. 



In the Diptera the Empididae are well known to be predaceous, capturing other 

 insects upon the wing. Wahlberg, in an interesting paper on the mosquitoes of 



