Attached to the “prothorax” is a rather long, pointed, and very elastic projection exactly corresponding with the tongue of the Skip-jack. The end of this tongue fits into a groove in the “sternum.”
When the beetle falls on its back, it curves its body as shown in the illustration, the tongue thus being freed from its groove. It then smartly springs the tongue back into its place with the sharp clicking sound already referred to, and does so with such force that it leaps into the air to some height.
Generally it falls on its feet, but if it should fail, it repeats the process. If one of these beetles be laid on a plate or similar smooth surface, it will skip ten or twelve times without stopping, and after a short rest will begin again.
There are some curious little beings, popularly called Spring-tails, which afford excellent examples of the Leaping Spring. Their exact place in the system of Nature is rather uncertain, some zoologists considering them as insects, while strict entomologists reject them. They are very small, and mostly of a darkish brown colour.
Plenty of them may be found under stones in damp spots, under bark, and in similar localities, though they are often found in houses, and have frequently traversed the paper on which I have been writing this book. Cellars are favourite localities of theirs, and a little flour sprinkled on a plate or piece of paper in a cellar is tolerably sure to attract them. Although they are certainly not more than the fifteenth of an inch in length, they may be at once recognised by their peculiar attitude, which very much resembles that of a dog or cat in its usual sitting posture.
As long as they are not disturbed they crawl about in a quiet manner, but if touched, or even alarmed, they suddenly make a tremendous leap, propelling themselves by means of a forked and elastic tail, doubled under their bodies, and acting just like the tongue of a Skip-jack.
Below the Skip-jack Beetle is shown the common Grasshopper, as an example of muscular leaping springs.
We all know what wonderful leaps the Grasshopper, Cricket, and all their kin can make, the leaping movement being evidently intended more as a means of defence than as an ordinary mode of locomotion. The same may be observed in the Kangaroos and Gerboas, which are content to use an ordinary walking pace when undisturbed, but when alarmed can make tremendous leaps, and outstrip almost any pursuer.
Even in Man, the Horse, the Dog, &c., which are most essentially leaping animals, the same principle is employed, the legs being used as muscular springs acted upon by the will of the owner.