THE DIPTERA OR FLIES 47 



readily be distinguished from the females by their longer 

 labial palpi, large, bushy antennae and by having clasping 

 organs at the posterior end of the body. In the great 

 majority of species they are not blood suckers like the 

 females, but content themselves with a vegetarian diet 

 by sucking the juices of plants. For this reason and also 

 because they are short lived, they are much less in evidence 

 than the females. 



It has been abundantly shown that the bite of mosqui- 

 toes of the genus Anopheles forms the sole means for the 

 introduction of malaria into the human system. As will 

 be more fully described in a later chapter the germs of 



PIG. 38. Anopheles at left, Culex at right in characteristic resting 



position. 



malaria are introduced into the body with the fluid the 

 mosquito injects from its salivary glands while it is suck- 

 ing blood. In a similar way another much dreaded dis- 

 ease, yellow fever, is carried by mosquitoes of the genus 

 Aedes (Stegomyia). By getting rid of disease-carrying 

 mosquitoes, therefore, the liability of these diseases 

 to spread becomes greatly reduced, and much attention 

 has been given in recent years to devising efficient means 

 of exterminating these insects. Draining swamps and 

 marshes where mosquitoes breed is often resorted to, and 

 where this is not feasible, covering the surface with a thin 

 film of kerosene oil is often tried. Kerosene quickly kills 

 the larvae when they come to the surface to breathe, and 

 while it may have to be put on the water more than once 



