446 Because of the large angle through which it can rotate and because of its angle to the body, the foreleg is most important as a lever. In contrast, the mid- and hindlegs, which each rotate through only a small angle, exert only a slight lever effect and serve primarily as struts (in the fully extended, rigid position). For the foreleg in its fully protracted position, contraction of the retractor muscle (i.e., the lever effect) will be sufficient to overcome the opposing retarding (strut) effect and, provided that the frictional forces between the ground and tarsi are sufficient, the body will be moved forward.

However, the largest component of the propulsive force is derived as a result of the leg's ability to flex and extend by virtue of their jointed nature. Flexure (a decrease in the angle between adjacent leg segments) will raise the leg off the ground so that it can be moved forward without the need to overcome frictional forces between it and the ground. In the case of the foreleg, flexure first will remove, by lifting the leg from the ground, the retarding effect as a result of its action as a strut and, second, when the leg is replaced on the substrate, will cause the body to be pulled forward. Flexure of the foreleg continues until the leg is perpendicular to the body, at which point extension begins so that now the body is pushed forward. For the mid- and hindlegs, flexure serves to bring the legs into a new forward position. Extension, as in the case of the foreleg, will push the body forward. Because the hindleg is usually the largest of the three, it exerts the greatest propulsive force.

As noted above, the horizontal axial force along each leg has a transverse as well as a longitudinal component. Thus, as an insect moves, its body zigzags slightly from side to side, the transverse forces exerted by the fore- and hindlegs of one side being balanced by an opposite force exerted by the middle leg of the opposite side in the normal rhythm of leg movements.

Rhythms of Leg Movements. Most insects use all six legs during normal walking. Other species habitually employ only the two anterior or the two posterior pairs of legs but may use all legs at higher speeds. In all instances, however, the legs are lifted in an orderly sequence (though this may vary with the speed of the insect), and there are always at least three points of contact with the substrate forming a "triangle of support" for the body. (In some species that employ two pairs of legs, the tip of the abdomen may serve as a point of support.) Two other generalizations that may be made are (1) no leg is lifted until the leg behind has taken up a supporting position and (2) the legs of a segment alternate in their movements.

In the typical hexapodal gait at low speed, only one leg at a time is raised off the ground, so that the stepping sequence is R3, R2, Rl, L3, L2, Ll (where R and L are right and left legs, respectively, and 1, 2, and 3 indicate the fore-, mid-, and hindlegs, respectively). With increase in speed, overlap occurs between both sides so that the sequence first becomes R3 Ll, R2, Rl L3, L2, etc., and, then, R3 Rl L2, R2 L3 Ll, etc., that is, a true alternating tripodal gait.

The orthopteran Rhipipteryx has a quadrupedal gait, using only the anterior two pairs of legs and using the tip of the abdomen as a support. Its stepping sequence is Rl L2, R2 LI., etc. Mantids are likewise quadrupedal at low speed, using the posterior two pairs of legs (sequence R3 L2, R2 L3, etc.). At high speed, the forelegs are brought into action though the insects remain effectively quadrupedal (sequence Ll R3, L3 R2, L2 R1, etc.).

A variety of methods for turning have been observed, often in the same species. They include increasing the length of the stride on the outside of the turn, increasing the frequency of stepping on the outside of the turn, fixing one or more of the "inside" legs as pivots, and moving the legs on the inside of the turn backward.

Coordination of the movements both among segments of the same leg and among different legs requires a high level of neural activity, both sensory and motor. Like other

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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