234 THE HAUNTS OF LIFE 



minute, but many an insect, such as a humble- 

 bee, vibrates its wings 200 times in a second. 

 In most cases the hum or buzz is simply due 

 to the rapidity with which the wings strike the 

 air, and there is no structure, visible to the 

 naked eye, in the animal kingdom that moves 

 so rapidly as an insect's wing. When the 

 wings are large, as in dragon-flies and big 

 butterflies, the number of strokes in a second 

 is small. There is a fossil dragon-fly whose 

 wings taken together have a span of 2 feet 

 from one side to another, but there is nothing 

 like this to-day. 



Insects vary greatly in their power of flight. 

 Many of the two-winged insects cannot fly 

 more than a few hundred yards, and can hardly 

 steer themselves at all, but are borne along by 

 the wind. This is true, for instance, of the 

 mosquitoes, the bite of which in some countries 

 often causes malarial fever. It is true also of 

 our common house-fly, which may cause disease 

 such as typhoid fever, by walking on our food 

 with dirty feet for it revels in decaying matter, 

 and may come straight from a refuse-heap to 

 our jam-dishes and milk-jugs, carrying with it 

 disease-germs which find there highly favour- 

 able conditions for multiplying rapidly. 



