Function

The majority of insectan legs are either elongate, slender, and designed for walking and climbing or cursorial, i.e., adapted for running, as in the cockroach (Fig. 1A). During walking, the legs form alternating triangles of support, with the fore and hind legs of one side and the middle leg of the opposite side contacting the substrate as the other three legs move forward. Various modifications allow the legs to be used in other forms of locomotion. Enlarged hind legs of many Orthoptera, fleas, and other insects are saltatorial, meaning they are designed for jumping. The jump of insects such as fleas is aided by a rubberlike protein called resilin in the cuticle that stores and subsequently releases energy for the jump. Powerful, spadelike forelegs of mole crickets, scarab beetles, burrowing mayflies, and other insects are fossorial, or adapted for digging and rapid burrowing (Fig. 1B). Flattened, fringed legs of aquatic insects such as dytiscid and gyrinid beetles and notonectid backswim-mers serve as oars for paddling or swimming (natatorial legs), while long legs with hydrophobic tarsal hairs and anteapical claws, as seen in water striders (Gerridae), are for skating on the surface of water. The legs of some insects, although well developed, have lost their associated locomotory function. The spiny legs of Odonata, for example, are designed for perching or seizing and holding prey captured while the dragonfly is in flight; the legs are ineffectual for walking.

FIGURE 1 (A) Cursorial foreleg of the Madeira cockroach (Leucophaea maderae). Illustration by T. S. Vshivkova. (B) Fossorial foreleg of the northern mole cricket (Neocurtilla hexadactyla). Illustration by T. S. Vshivkova.
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