MOTIONS OF INSECTS. 449 
In walking and running, the hexapods, like the larve that nave 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!; but this is 
contrary to fact, and indeed would make their ordinary motions, instead of 
walking and running, akind 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 (Ivodes 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 antenne 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.? 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.® I have often noticed a millepede 
(Iulus 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 ata 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, soas 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 (Scolopendra), as well as that of 
this insect and its congeners, is retrogressive as well as progressive. Put 
your finger to the common one (Lithobius forjficalus), 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. 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.‘ 
Insects vary much in their walking paces : some crawling along, others 
walking slowly, and others moying with a very quick step. The field- 
cricket (Gryllus campestris) creeps very slowly —the bloody-nose beetle 
(Timarcha tenebricosa) and the oil-beetle (Meloe Proscarabeus) march yery 
leisurely ; the spider wasps (Pompilus) walk by starts, as it were, vibrating 
their wings at the same time without expanding them ; while flies, ichnen 
mons, wasps, &c., and many beetles, walk as fast as they can, One insect, 
1 De Geer, iii, 284. 2 Hist. Ins. 10. 
5 Redi, Opuse. i. 80. Amoreux, 44, 4 Gurr, ii. 426 
GQ 
