“For an examination of the gait of insects, we choose, for obvious reasons, those which have very long legs and which at the same time are slow walkers.
“Insects may be called ‘double-three-footed,’ from the manner in which they alternately place their legs. There are always three legs set in motion at the same time, or nearly so, while in the meantime the remaining legs support the body, after which they change places.
FIG. 122.—The same by the left fore (_l_{ 1}_), middle (_l_{ 2}_), and hind, leg (_l_{ 3}_) of a Carabus. Natural size. ]
FIG. 123.-Tracks of a _Blaps mortisaga_ marked by the differently painted tibial points: ●, tracks of fore, —○, middle, —/, hind leg. Natural size. ]
FIG. 124.—Tracks of _Necrophorus vespilio_. Natural size. ]
“To be more exact, it is usually thus: At first (Fig. 118) the left fore leg (_L_{ 1}_) steps out, then follows the right middle leg (_R_{ 2}_), and the left hind leg (_L_{ 3}_). Then while the left fore leg begins to retract and thus make the backward movement, the right fore leg is extended, whereupon the left middle leg and the right hind leg are raised in the same order as the first three feet.”
Graber[23] painted the feet of beetles and let them run over paper, and goes on to say:
“Let us first pursue the tracks of the Blaps, for example (Fig. 123). Let the insect begin its motion. The left fore leg stands at _a_, the right middle leg at β, and the left hind leg at _c_. The corresponding number of the other set of three feet at α, _b_, γ. At the first step the three feet first mentioned advance to _a′_β′_c′_, the second set on the other hand to α′_b′_γ′. Thereby the tracks made by the successive steps fall quite, or almost quite, on each other, as appear also in the tracks of a burying beetle (Fig. 124).
“As the fore legs are directed forward and the hind legs backward, while the middle legs are placed obliquely, the reason of the more marked impressions of the latter is evident.
“The highest testimony to the precise exactitude and accuracy of the walking mechanism of insects is furnished by the fact that in most insects, and particularly in those most fleet of foot, which, whether they are running away or chasing their prey, must be able to rely entirely upon their means of locomotion;—the fact, we say, that whether they desire to move slowly or more quickly, the distances of the steps, measured by the length as well as by the cross-direction, hardly differ a hair’s breadth from one another, and this is also the case when the tarsi are cut off and the insects are obliged to run on the points of their heels (tibiæ).