122 



ANIMALS OF LAND AND SEA 



incomparably more rapid than that of birds. The common 

 cabbage butterfly moves its wings at the rate of 540 strokes 

 per minute; the sphingid moths at the rate of 4,320 beats per 



minute; the wasp 

 at the rate of 6,600 

 beats per minute; 

 the honey bee at the 

 rate of 11,400 beats 

 per minute; while 

 the wings of the 

 common house-fly 

 vibrate at the rate 

 of 19,800 beats per 

 minute. 



The difference in 

 the relative area of 

 the wings between 

 a mosquito and a 

 stork may be appre- 

 ciated when it is 

 realized that if a 

 stork had wings pro- 

 portionately as large 

 as those of a mos- 

 quito they would 

 have an area of al- 

 most twenty-eight 

 and a half square 

 yards, and an ex- 

 panse of more than 

 twenty-five feet. 

 Of afl the insects 

 the larger dragon-flies, so common about the ponds and streams 

 in which they live when young, are the swiftest on the wing. 

 One sort of these (AustropJilebia) was timed by Dr. R. J. Till- 

 yard, who found that it covered between 80 and 90 yards in 



Figs. 262-272. Flies commonly found in houses. 

 For explanations of the figures see p. xix. 



