Fig. 8. The means of the mean values for all crabs were used to estimate the forces acting on the body of a crab using different postures in various flow conditions. Fluid motion relative to the crab is right-to-left. Longer arrows represent larger forces. In air, crabs are shown only in the terrestrial posture. W_app, apparent weight (= weight-buoyancy); A, acceleration reaction; D, drag; L, lift. (A) Crab is locomoting through still fluid (water or air). Fastest punting speed in water=0.67ms^-1. Fastest recorded run on land=1.4ms^-1. Crab is locomoting at +4° angle of attack. Body acceleration=1.13ms^-1. (B) Crab is standing in moving fluid (water or air). Fastest water flow measured in the field at wave-swept site=1.6ms^-1, acceleration=1.71ms^-2. Air speed in hurricane 45ms^-1. Crab is standing with 0° angle of attack relative to oncoming flow. Acceleration reaction force was not calculated in the terrestrial hurricane condition because acceleration data appropriate to the size scale of a crab was not available. Note that a crab locomoting in water at its fastest punting speed generates positive lift greater than its effective weight if the crab uses a +4° angle of attack.