MOTIONS OF INSECTS. 433 



I shall begin the list of lualkers, the movements of which are aided by 

 various instruments, with one which is well known to most people, — the 

 grub of the nut-weevil {Balaninus Nucum). When placed upon a table, 

 after lying some time, perhaps, bent in a bow, with its head touching its 

 tail, at last it begins to move, which, though in no certain direction, it does 

 with more speed than might be expected. Rosel fancied that this animal 

 had feet furnished with claws ; but in this, as De Geer justly observes, he 

 was altogether mistaken, since it has not the least rudiment of them, its 

 motion being produced solely by the alternate contraction and extension 

 of the segments of the body, assisted, perhaps, by the fleshy prominences 

 of its sides. Other larvae have this annular motion aided by a slimy secre- 

 tion, which gives them further hold upon the plane on which they are 

 moving, and supplies in some degree the place of legs or claws. That of 

 the weevil of the common figwort {Clonus ScropJndarice) is always covered 

 with slime, which enables it, though it renders its appearance disgusting, 

 to walk with steadiness, by the mere lengthening and shortening of its 

 segments, upon the leaves of that plant.^ Of this kind, also, are those 

 larvae, mentioned above, received by De Geer from M. Ziervogel, whicli, 

 adhering to each other by a slimy secretion, glide along so slowly upon 

 the ground as to be a quarter of an hour in going the breadth of the hand : 

 whence the natives call their bands G'drds-drag? 



As a further help, others again call in the assistance of their ungiiiform 

 mandibles. These, which are peculiar to grubs with a variable membrana- 

 ceous, or rather retractile head*, especially those of the fly tribe (Mtiscidce), 

 when the animal does not use them, are retracted not only within the head, 

 but even within the segments behind it* ; but when it is moving, they are 

 protruded, and lay hold of the surface on which it is placed. They were 

 long ago noticed by the accurate Ray. " This blackness in the head," 

 says he, speaking of the maggot of the common flesh-fly, " is caused by 

 two black spines or hooks, which when in motion it puts forth, and fixing 

 them in the ground, so drags along its body." * The larvas of the aphidi- 

 vorous flies (Sccsva, &c.), the ravages of which amongst the Aphides 1 have 

 before described to you, transport themselves from place to place in the 

 same way, walking by means of their teeth. Fixing their hind part to the 

 substances on which they are moving, they give their body its greatest 

 possible tension ; and, if I may so speak, thus take as long a step as they 

 can : next laying hold of it with their mandibles, by setting free the tail, 

 and relaxing the tension, the former is brought near the head. Thus the 

 animal proceeds, and thus will even walk upon glass.® Some grubs, as 

 those of the lesser house-fly (Anthomi/ia canicidaris), have only one of these 

 claw-teeth ; and in some they have the form as well as the office of legs.'' 

 Bonnet mentions an apodous larva, that, before it can use its mandibles, is 

 obliged to spin, at certain intervals, little hillocks or steps of silk, of which 

 it then lays hold by them, and so drags itself along. 



Besides their mandibular hooks, some of these grubs supply the want of 



1 De Geer, v. 210. 2 ibid. vi. 338. 



3 See MacLeay in Philos. Mag. &c., N. Ser. No. 9. 178. 



4 De Geer, vi. 65. 



6 Hist. Ins. 270. ® Reaumur, iii. 369. 



7 De Geer, vi. 76. Eeaumur, iv. 376. Swamm. Bill. Nat. lid. Hill, ii. 40. a. t. 

 xxxix. f. 3. h. h. 



