16 Mosquitoes and 
to the walls, and also the beds, clothing and persons of the 
soldiers.* 
Fumigants. —As an alternative to spraying, fumigation may 
be employed in order to rid rooms of mosquitoes. Cresyl has 
been recommended as a good fumigant; the quantity required is 
about 75 grains for every 35 cubic feet of space, and it need only 
be left to volatilise in the closed room. It has the advantage of 
being innocuous to human beings. 
Natural Enemies. —A great variety of other animals are 
known to prey upon adult mosquitoes, such as predaceous flies, 
wasps, dragonflies, spiders, lizards, birds and bats. The value of 
swallows was recognised even at the end of the eighteenth 
century, when the Commune of Marsciano (Umbria) asked for a 
papal decree prohibiting the destruction of these birds, on the 
ground that their being killed in large numbers for food caused 
an increase in the number of noxious winged insects and so made 
the place unhealthy. Experiments have recently been made in 
the United States as to the cultivation of bats on a large scale for 
the purpose of keeping down mosquitoes ; it is said that the 
results were good, and that the value of the bat guano covered the 
expense. 
DESTRUCTION OF LARVAE AND BREEDING PLACES. 
The destruction of mosquito larvae or of places where they are 
likely to live is much the most satisfactory way of dealing with 
these pests. The general principles adopted in this method of 
attack are : (i) the removal of possible breeding places; (ii) the 
effective screening of collections of water which cannot be removed ; 
(iii) the utilisation of natural enemies, which are numerous ; (iv) 
where these methods are not practicable, and for supplementing 
them, the application of larvicides, either in the form of oil which 
will form a film on the surface of the water and so prevent the 
larvae from reaching the surface to breathe, or of substances which, 
when mixed with the water, will kill the larvae. 
The great diversity of the breeding habits of mosquitoes has 
already been referred to, and it is obvious that each of the classes 
* For an account of the preparation and properties of this liquid, vide 
“ Review of Applied Entomology,” Yol. Ill, ser. B, July 1915, pp. 105-106. 
