MOTIONS OF INSECTS. 505 



instance, have their wings most covered with nervures. The wings of 

 insects in flying, Hke those of other flying animals, you are to observe, 

 move vertically, or up and down. 



In considering the flight of insects, I shall treat of that of each order 

 separately, beginning with the Coleoptera or beetles. Their subsidiary 

 instruments of flight are their wing-cases (elytra), and in one instance 

 winglets (alula). The former, which in some are of a hard horny sub- 

 stance, and in others are softer and more like leather, though they are kept 

 immovable in flight, are probably, by their resistance to the air, not with- 

 out their use on this occasion. The winglets are small concavo-convex 

 scales, of a stiff membranaceous substance, generally fringed at their 

 extremity. I know at present of only one coleopterous insect that has 

 them (Dytiscus marginalis). They are placed under the elytra at their 

 base. Their use is unknown ; but it may probably be connected with 

 their flight. The wings of beetles are usually very ample, often of a 

 substance between parchment and membrane. The nervures that traverse 

 and extend them, though not numerous, are stronger and larger than 

 those in the wings of insects of the other orders, and are so dispersed as 

 to give perfect tension to the organ. When at rest — except in Molorchus, 

 Atractocerus, Necydalis, and some other genera — they are folded trans- 

 versely under the elytra, generally near the middle, with a lateral longi- 

 tudinal fold, but occasionally near the extremity. When they prepare for 

 flight, their antennas being set out, the elytra are opened so as to form an 

 angle with the body and admit the free play of the wings ; and they 

 then fly off, striking the air by the vertical motion of these organs, the 

 elytra all the while remaining immovable. The Cetona, however, as 

 noticed by M. Audouin, differ from most if not all other coleopterous 

 insects in keeping their elytra closed during their flight.'^ During their flight 

 the bodies of insects of this order, as far as I have observed them, are always 

 in a position nearly vertical, which gives to the larger sorts, the stag-beetle 

 for instance, a very singular appearance. Olivier, probably having some 

 of the larger and heavier beetles in his eye, affirms that the wings of 

 insects of this order are not usually proportioned to the weight of their 

 bodies, and that the muscular apparatus that moves them is deficient in 

 force. In consequence of which, he observes, they take flight with diffi- 

 culty, and fly very badly. The strokes of their wings being frequent, 

 and their flight short, uncertain, heavy, and laborious, they can use their 

 wings only in very calm weather, the least wind beating them down. 

 Yet he allows that others, whose body is lighter, rise into the air and fly 

 with a little more ease, especially when the weather is warm and dry ; 

 their flights, however, being short, though frequent. He asserts also, that 

 no coleopterous insect can fly against the wind.^ These observations may 

 hold, perhaps, with respect to many species ; but they will by no means 

 apply generally. The cockchafer (Mdontha vulgaris), if thrown into 

 the air in the evening, its time of flight, will take wing before it falls to 

 the ground. The common dung-chafer (Geoirupes stercorarius) — wheel- 

 ing from side to side like the humble-bee — flies with great rapidity and 

 force, and, with all its dung-devouring confederates, directs its flight with 

 the utmost certainty, and probably often against the wind, to its food. The 



' Ann. Soc. Ent. de France, viii. p. xlviii. ^ Entomol. i. 1. 



43 



