MOTIONS OF INSECTS. 449 



In walking and running, the hexapods, like the larvae that have perfect 

 legs, move the anterior and posterior leg of one side and the intermediate 

 of the other alternately, as I have often witnessed. De Geer, however, 

 affirms that they advance each pair of legs at the same time l ; but this is 

 contrary to fact, and indeed would make their ordinary motions, instead of 

 walking and running, a kind of canter and gallop. Whether those that have 

 more than six feet move in this way, which is not improbable, from the dif- 

 ficulty of attending at the same time to the movements of so many mem- 

 bers, is not easily ascertained. 



. The dog-tick (Ixodes Ricinus), if when young and active it moves in 

 the same way that it does when swollen to an enormous size with blood, 

 seems to afford an exception to the mode of walking just described. It 

 first uses, says Ray, its two anterior legs as antennae to feel out its way, 

 and then fixing them, brings the next pair beyond them, which being also 

 fixed, it takes a second step with the anterior, and so drags its bloated 

 carcass along. 2 Redi observes that when scorpions walk they use those 

 remarkable comb-like processes at the base of their posterior legs to assist 

 them in their motions, extending them and setting them out from the 

 body, as if they were wings: and his observation is confirmed by Amoreux, 

 who calls them ventral swimmers. 3 I have often noticed a millepede 

 (lulus terrestris\ frequently found under the bark of trees, and where 

 there is not a free circulation of air, the motions of which are worthy of 

 attention. Observed at a little distance, it seems to glide over the surface, 

 like a serpent, without legs ; but a nearer inspection shows how its move- 

 ment is accomplished. Alternate portions of its numerous legs are ex- 

 tended beyond the line of the body, so as to form an obtuse angle with it ; 

 while those in the intervals preserve a vertical direction, so that as long 

 as it keeps moving, little bunches of the legs are alternately in and out from 

 one end to the other of its long body ; and an amusing sight it is to see the 

 undulating line of motion successively beginning at the head and passing 

 off at the tail. The motion of centipedes (Scolopendrd), as well as that of 

 this insect and its congeners, is retrogressive as well as progressive. Put 

 your finger to the common one (Lithobius forficatus), and it will imme- 

 diately retrograde, and with the same facility as if it was going forwards. 

 This difference, however, is then observable it uses its four hind legs, 

 which, when it moves in the usual way, are dragged after it. Almost all 

 the other apterous insects, as well as many of those in the other orders, can 

 move in all directions ; backwards, and towards both sides, as well as for- 

 wards. 4 Bonnet mentions a spider (not a spinner) that always walked 

 backwards when it attacked a large insect of its own tribe ; but when it 

 had succeeded in driving it from a captive fly, which, however, it did not 

 eat, it walked forwards in the ordinary way. 4 



Insects vary much in their walking paces : some crawling along, others 

 walking slowly, and others moving with a very quick step. The field- 

 cricket (Gryllus campestm) creeps very slowly the bloody-nose beetle 

 (Timarcha tenebricosa) and the oil-beetle (Meloe Proscarabceus) march very 

 leisurely ; the spider wasps (Pompilus) walk by starts, as it were, vibrating 

 their wings at the same time without expanding them ; while flies, ichneu- 

 mons, wasps, &c., and many beetles, walk as fast as they can. One insect, 



i De Geer, iii. 284 2 Hut. Ins. 10. 



3 Redi, Opusc. i. 80. Amoreux, 44. <* (Eitvr. ii. 426. 



G G 



