286 



MOTIONS OF INSECTS. 



Africa, 500 miles distant — a striking proof of its powers 

 of wing. 1 The species of the genus Agrion 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 colours of different 

 individuals, form no uninteresting object during a summer 

 stroll. With respect to the mode of flight of the other neu- 

 ropterous tribes I have nothing to remark ; for that of the 

 Ephemerae, which has been most noticed, I shall consider under 

 another head. 



The next order of insects, the Hymenoptera, attract also 

 general attention as fliers, and from our earliest years. The 

 ferocious hornet, with its trumpet of terror ; the intrusive and 

 indomitable wasp ; the booming and pacific humble-bee, the 

 frequent prey of merciless schoolboys; and that universal 

 favourite, the industrious inhabitant of the hive, — all be- 

 longing to it, — are familiar to every one; 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. 2 

 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. 3 



1 Entom. Mag. v. 251. 2 Jurine, Hymenopt. t. 2 — 5. 



3 Kirby, Mon. Ap. Angl. i. 96. 108. t. xiii. f. 19. 



