466 MOTIONS OF INSECTS. 



I shall begin the list of walkers, the movements of which are aided 

 by various instruments, with one which is well kn'own 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 Gear 

 justly observes, he was altogether mistaken, since it has not the least 

 rudiment of them, its motion being produced solely by the alternate con- 

 traction 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 secretion, 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 (Cioniis Scrophu- 

 larict) is always covered with slime, whicii 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, which, 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 Gdrds-drag.^ 



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

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

 naceous, or rather retractile head-', especially those of the fly tribe (^Mus- 

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

 the head, but even within the segments behind ii^; 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 larva; of 

 the aphidivorous flies (^Scfeva, &,c.), the ravages of which amongst the 

 Aphides I 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 (^Anthomyia ca)iiciilaris),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 legs by means of claws at their anus. Thus that of the flesh-fly, 



> De Geer, v. 210. « Ibid. vi. 338. 



» See MacLeay in Philos. Mag. fee. N. Ser. No. 9. 178. 



* De Geer, vi. 65. » Hist. Ins. 270. « Reaumur, iii. 369. 



7 De Geer, vi. 76. Reaumur, iv. 376. Swamm. Bibl. A'at. Ed. Hill, ii. 46. a. t. xxiix. 

 f. 3. h. h. 



