Fig. 6. Calculated contribution to drag on the crab due to drag on the swinging of one leg. Positive drag indicates drag acting in the opposite direction from the direction the whole crab is moving through the water (i.e. resisting forward movement). Negative drag indicates drag acting in the same direction as the crab is moving through the water (aiding forward movement). Filled circles indicate calculated drag on a crab model with legs not swinging. Open circles indicate the calculated drag on a crab model when adjusted for the contribution of one swinging leg. Grey triangles indicate the adjustment in drag due to one swinging leg. A, the time when a leg is not swinging relative to the body; B, the time when a leg is in the stance phase, generating thrust against the substratum and thus swinging with respect to the body; C, the time when a leg is in the swing phase and swinging with respect to the body.