ANIMAL FLIGHT 1 25 



and the hind wings membranous and closing like a fan instead 

 of being folded on a hinge in the front margin as in the beetles. 

 In most the flight is weak and rattly, and very many cannot 

 fly at all. But some, like the migratory locusts, are strong fliers. 



Regarding the speed of grasshoppers I quote a letter from 

 Mr. Andrew N. Caudell. 



"In early August of 1920 while studying economic species of 

 grasshoppers in Centennial Valley, Montana, I had an excellent 

 opportunity of observing the speed at which Cannula pellucida 

 flew. By noting individuals that were flushed by the roadside 

 by the automobile in which I was riding I chose ones that flew 

 parallel with the machine, which was driven at the rate of 15 

 miles per hour. I found that under those conditions the rate of 

 flight for this species is almost exactly 15 miles per hour. In 

 long flights, especially with the wind, the rate may be much 

 faster, as J. R. Parker has estimated the speed of migratory 

 swarms to be 30 miles per hour. That appears to be too high 

 an estimate, judging from my experience with the insects' flight 

 when flushed by the automobfle. Mr. C. L. Corkins gives the 

 rate of flight of Melanoplus atlantis as 20 miles per hour, the 

 rate being determined by the same method I used with Can- 

 nula, that is by observations made from an automobile moving 

 at a given rate." 



The flies properly so called, the house-fly, the blue-bottle, 

 the horse-fly, the crane-fly, the black-fly, the mosquito, the 

 gnat, the midge, the robber-fly, etc., have only two wings, the 

 hinder pair being replaced by curious knobbed structures known 

 as balancers or halteres which are apparently sensory and in 

 some kinds possibly stridulating. It is interesting to note that 

 while in the beetles the hind wings only are used for flight, in 

 the flies these have completely lost their function as flying 

 organs, the flight being efi'ected entirely by those of the anterior 

 pair. 



While a few flies are wingless, or have very small and useless 

 wings, most of them are expert fliers. They can twist and turn 

 and dodge and hover and dart quite as well as the dragon-flies, 



