FLIGHT OF INSECTS. 319 



These scales doubtless contribute to the protec- 

 tion of the wing ; but they at the same time add 

 considerably to their weight, and impede the velo- 

 city of their action. This inconvenience appears 

 to have been in a great measure compensated by 

 the greater size of the wings, and by the extent of 

 the surface with which they strike the air. Still, 

 however, it is sufficiently obvious that insects of 

 this order fly with less rapidity and steadiness 

 than most others.* But this unsteadiness, again, 

 is turned to good account ; for the butterfly, by its 

 irregular and apparently capricious movements, 

 alternately dipping and rising in the air, so as to 

 describe a series of zig-zag lines, more easily eludes 

 capture when pursued, not only by naturalists, but 

 also by birds, that are eagerly seeking to catch 

 them. It is astonishing to what a distance the silk 

 worm moths will fly : some have been known to 

 travel more than a hundred miles in a short time. 

 The Apatura Iris (Fab.) often rises to so great a 

 height in the air as to be quite invisible. 



A mechanical contrivance is adopted in many of 

 the Lepidoptera for connecting the wings together, 

 and keeping them more steady during flight. It 

 consists of a horny process, w^hich projects out- 

 wards from the base of the upper margin of the 

 lower wing, and is received into a hook in the 

 under edge of the upper wing. Sometimes two or 

 three bristles are substituted for the horny process. 

 By this mechanism all the wings are locked toge- 

 ther, and brought into action at the same time.f 



* Notable exceptions occur to this rule, in Sphinges, Sesice, and 

 EgericB, wliich are all insects of very rapid flight. 



t De Geer, Memoires pour servir a I'Histoiredes Insectes, i. i7,'3, 



