62 The Honey-Makers 



spiracles when the wings are raised, filling the air-sacs in 

 the body, lessening the specific gravity of the insect and 

 enabling it to rise in the air and remain there with but 

 slight muscular exertion. At the first stroke of the wings 

 the spiracles are closed and the air retained. 



Girard says that inside each spiracle is a muscular valve 

 that by opening or closing can let in or shut out the air, 

 and that this is under the control of the insect, who can thus 

 at will fill the air-sacs and decrease the specific gravity. 



Thus we find the breathing apparatus of the bee com- 

 plex in structure and varied in function. It serves to 

 aerate the blood and at the same time to make effective 

 the action of the wings. 



Rapidity of respiration affects the temperature of the 

 insect. The bumble-bee, according to Newport, raises its 

 temperature by quickened respiration, and does this volun- 

 tarily in order to generate heat for purposes of incubation. 



Doubtless the enclosed air, which is shut at the will of 

 the bee into the air-sacs during flight, is heated by its body, 

 thus becoming lighter, and acting as the gas in a balloon to 

 increase the buoyancy. 



The bee cannot fly until its air-sacs are filled ; conse- 

 quently when one which has been sleeping is suddenly 

 roused, it cannot at once fly away, but makes a series of 

 " hops," or little jumps, fanning its wings rapidly the while 

 until the air-sacs are expanded with air and its body is in 

 a condition for flight. 



The pitch of the bee's wing music depends upon the 

 rapidity with which the wings vibrate, and it was this pitch 

 from the wings of an excited bee that gave foundation to 

 the declaration that the wings sometimes move at the rate 

 of more than four hundred times a second. As a rule, 

 however, they move considerably slower than this, the 

 maximum rate of vibrations soon inducing exhaustion. 



