90 FLYING BACKWARDS 



moment the wings are inclined, ever so 

 slightly, in a backward direction, motive power 

 is engendered and, without wing acceleration, 

 the fly darts off into space. 



One can understand that a very slight 

 alteration in the set of the wings is sufficient 

 to effect these movements. The hover-fly is 

 capable, not only of poising, but can turn 

 without moving from the spot, or advance 

 slowly and cautiously ; and again, what is 

 more extraordinary, the fly is capable of 

 moving backwards. This indeed is a feat 

 possible only to creatures possessing " high 

 pressure " flight, which includes genuine 

 humming-birds. 



I am unable to speak from personal observa- 

 tion, but I imagine that a humming-bird is 

 also capable of coming out backwards from 

 a cramped position, say, a tubular flower- 

 head (?). The act of retrogression is never 

 continued beyond the actual necessities of 

 the case, but may be distinctly observed in 

 respect to bombylius ; the hawk-moths (stel- 

 latarum, fusiformis and bombyliformis) ; and 

 almost certainly in the cases of the larger 

 hawk-moths (celerio, elpenor, convolvuh, etc.); 

 but as these fly at dusk it is difficult to 

 take rehable observations. According to my 

 theory, backward movement would obtain 



