MOTIONS OF INSECTS. 509 



ticularly in ^shna and Libellula, and such the force of the muscles that 

 move them, that they seem never to be wearied with flying. I have 

 observed one of the former genus (Anax imperator Leach) sailing for 

 hours over a piece of water — sometimes to and fro, and sometimes wheel- 

 ing from side to side ; and all the while chasing, capturing, and devouring 

 the various insects that came athwart its course, or driving away its com- 

 petitors — without ever seeming tired, or inclined to alight. Another 

 species (^jEshna variegata), very common in lanes and along hedges, 

 which flies, like the Orthoptera, in a waving line, is equally alert and 

 active after its prey. This, however, often alights for a moment, and 

 then resumes its gay excursive flights. A Libellula, resembling this last 

 insect, flew on board the vessel in which Mr. Davis was sailing, Dec. 11, 

 1837, when at sea, and the nearest land was the coast of Africa, 500 

 miles distant — a striking proof of its powers of wing.^ The species of 

 the geT^nsAgrion cut the air with less velocity ; but so rapid is the motion 

 of their wings that they become quite invisible. Hawking always about 

 for prey, the Agrions, from the variety of the colors of different indi- 

 viduals, form no uninteresting object during a summer stroll. With 

 respect to the mode of flight of the other neuropterous tribes I have 

 nothing to remark ; for that of the EphemercB, which has been most 

 noticed, I shall consider under another head. 



The next order of insects, the Hymenoptera, attract also general atten- 

 tion as fliers, and from our earliest years. The ferocious hornet, w^ith its 

 trumpet of terror ; the intrusive and indomitable wasp ; the booming and 

 pacific humble-bee, the frequent prey of merciless schoolboys ; and that 

 universal favorite, the industrious inhabitant of the hive, — all belonging 

 to it, — are familiar to everyone ; and in summer there is scarcely a flower 

 or leaf in field or garden, which is not visited by some of its numerous 

 tribes. The four wings of these insects, the upper pair of which are 

 larger than the under, vary much in their nervures. From the saw-flies 

 (^Serrifera) , whose wings are nearly as much reticulated as those of some 

 Neuroptera, to the minute Chalcis and Psilus, in which these organs are 

 without nervures, there is every intermediate variety of reticulation that 

 can be imagined.^ It has been observed that the nervures of the wings 

 are usually proportioned to the weight of the insect. Thus the saw-flies 

 have generally bodies thicker than those of most other Hymenoptera, 

 while those that have fewer nervures are more slender. This, however, 

 does not hold good in all cases — so that the dimensions and cut of the 

 wings, the strength of their nervures, and the force of their muscles, must 

 also be taken into consideration. The wings of many of these insects, 

 when expanded, are kept in the same plane by means of small hooks 

 {hamuli) in the anterior margin of the under wing, which lay hold of the 

 posterior margin of the upper."' Another peculiarity also distinguishes 

 them. Base covers (tegula), or small concavo-convex shields, protect 

 the base of the wings from injury"* or displacement. 



The most powerful fliers in this order are the humble-bees, which, like 

 the dung-chafers (Geotrupes), traverse the air in segments of a circle, the 



' Entom. Mag. r. 251. • Jurine, Hymenopt. t. 2 — 5. 



* Kirhy, Mtm. Ap. Avgl. i. 96. 108. t. xiii. f. 19. 



* Kirby, Uun. Ap. Angl. i. y6. 107. t. v. f. 8. d d. 



43* 



