164 MOSQUITOES OF NORTH AMERICA 
effect was apparent until the larve were about to pupate; then the worms, hav- 
ing probably completed their parasitic stage in the mosquito, leave the host. 
They break forth from the posterior end of the body by perforating the mem- 
brane surrounding the anus. The larger worm leaves first, the smaller follow- 
ing a little later, and the mosquito larva dies as a result of the injuries. The 
Mermis larve died some hours after leaving their host. In one catch all the 
mosquito larvae were infested, but parasitized lots of larvee were rare; only two 
out of 26 lots were infested and these came from water in trees. No parasites 
could be found in adult Aédes calopus and Gendre considered the infestation 
accidental. 
INSECT ENEMIES. 
Many insects and nearly all of the predatory aquatic forms that are able to 
master mosquito larvee, will feed upon them and they form an important article 
in the diet of many species. Most of these carnivorous insects, however, are 
not prolific breeders, and they seldom deposit their eggs except in rather per- 
manent pools; as a consequence their importance as mosquito destroyers is 
not so great, though nevertheless considerable. Mosquitoes breed practically 
unmolested in artificial receptacles for rain-water and in transient pools. 
The larve of the predatory water-beetles of the families Dytiscide and Hydro- 
philide eat many mosquito larve, although from their great activity these often 
escape and the beetle larvee derive the greater part of their subsistence from 
other forms. 
Dr. W. E. Britton, of New Haven, Conn., who has made careful study of the 
mosquito problem in Connecticut, has found that the larva of Hydrophilus 
obtusatus Say (Schwarz det.) is one of the important natural enemies of mos- 
quito larve in the vicinity of New Haven. 
One of us (Howard) has recorded an observation in the course of which he 
took a half gallon of water from a stagnant pool which was teeming with aquatic 
insects, including hundreds of mosquito larve. Among these insects were three 
Hydrophilid larve and in the course of a week these three larve devoured practi- 
cally all of the other animal life in the jar in which the half gallon of stagnant 
water had been placed. 
Dr. J. B. Smith thinks that the larve of the Dytiscide are among the greatest 
enemies of mosquitoes. He is inclined to attribute the comparative freedom 
from mosquitoes of the hilly section of New Jersey very largely to these insects, 
and he quotes an interesting observation by Doctor Johnson in support of this 
conclusion. He also notes an observation by Mr. Viereck in which one good- 
sized dytiscid larva was seen to devour 434 mosquito larvee in two days. Galli- 
Valerio and Rochaz de Jongh found that an adult water-beetle, Dytiscus mar- 
ginalis, although it had been previously fed with meat, destroyed great numbers 
of mosquito larve and pupe. Dr. Adolf Eysell states that a single, nearly full- 
grown, larva of Acilius sulcatus destroyed more than forty mosquito larve over 
night. 
Dr. Smith states that the Gyrinide or so-called “ whirligig beetles,” which live 
nearly wholly at the surface of the water, are great destroyers of mosquito larve ; 
