MOTIONS OF INSECTS. 



223 



by two black spines or hooks, which when in motion it puts 

 forth, and fixing them in the ground, so drags along its 

 body." 1 The larva3 of the aphidivorous flies (Scceva, &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. 2 Some grubs, as those of the lesser house-fly 

 (Anthomyia canicularis), have only one of these claw -teeth ; 

 and in some they have the form as well as the office of legs. 3 

 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, Bay tells us in the place just quoted, pushes 

 itself by the protruded spines of its tail. The larva, also, of 

 a long-legged gnat (IAmnobia replicata), which in that state 

 lives in the water, is furnished with these anal claws, which, 

 in conjunction with its annular tension and relaxation, and 

 the hooks of its mouth, assist it in walking over the aquatic 

 plants. 4 



A remarkable difference, according to their station, obtains 

 in the bots of gad-flies (CE 'strides) ; those that are subcu- 

 taneous ( Cuticolce Clark) having no unguiform mandibles ; 

 while those that are gastric (GastricolcB Clark), and those 

 that inhabit the maxillary sinuses of animals ( Cavicolce Clark), 

 are furnished with them. In this we evidently see Creative 

 Wisdom adapting means to their end, for the cuticular bots 



i Hist. Lis. 270. 



3 De Geer, vi. 76. Reaumur, iv. 376. 

 a. t. xxxix. f. 3. h. h. 



4 De Geer, vi. 355. 



2 Reaumur, iii. 369. 

 Swamm. Bill. Nat. Ed. Hill, ii. 46. 



