REPORT ON MOSQUITOES. 91 



lers. With their raptorial legs they nip the larva near the breath- 

 ing tube, then either drop or suck it. Quite a number were 

 nipped and dropped and, once dropped, they rose no more. Pupse, 

 both of Anopheles and Ciilex, were expert in evading the grasp 

 and were not readily caught. In less than an hour three Ranatra 

 killed and sucked ninety-eight larvae. It is a question whether 

 Ranatra would be useful in stagnant pools, because the specimens 

 used in the experiment could only be found in the clear water of 

 a lilv pond where, no doubt, they controlled the Anopheles; but 

 when put into the stagnant water which sollicitans inhabits, they 

 died." 



What Mr. V'iereck says in the last sentence expresses the prac- 

 tical limitation of the usefulness of all the insect enemies of 

 mosquito larvae ; they do not inhabit the temporary pools formed 

 by rains, overflows, tides or in other manners. Their life period 

 is too long to admit of their using such places, and in them the 

 \\Tigglers have the opportunity to develop undisturbed. It ex- 

 plains also why permanent bodies of water are relatively safe, 

 and why even a country with plenty of brooks and ponds may be 

 practically mosquito free. 



So far as our present knowledge goes, we can make no prac- 

 tical use of these insect enemies as against the pestiferous species. 

 All that we can do is to make natural conditions as favorable for 

 them as possible. 



This account of the natural enemies would be incomplete were 

 I to omit the mosc|uito enemies of the mosquitoes. The larva of 

 PsoropJiora ciliata. which is our largest species, feeds on other 

 wrigglers exclusively, and is feeding constantly. A dozen of 

 these specimens will clean out a jar, containing a hundred ex- 

 amples of pipiens in less than twenty-four hours, and will be 

 ready to eat each other if the stock is not promptly renewed. 

 Usually, when a pool contains any number of large PsoropJiora 

 larvae the Culex are few and become daily less. To be sure the 

 adult Psorophora also bites, but every such adult has prevented 

 the de\'elopment of at least 100 Culex, hence we can forgive some- 

 thing. 



The species of Corethra which do not bite, are also predatory 

 in character and prey upon mosquito larvae, reducing them to a 

 minimum in places where they occur. Unfortunately they are 

 local and sometimes very rare. 



The plant enemies, duckweed (Lenina) and the green thread- 

 like Spirogyra, have been referred to in another connection and 

 their method of checking moscjuito development has been de- 

 scribed. 



