Kunal Patel writes: (Does) the presence of an exoskeleton (in cockroaches) increase the efficiency of locomotion in comparison with the hydrostatic skeleton of worms?
Kunal, I assume you are referring to annelid and polychaete worms and not the larvae of insects (e.g. loopers and maggots) which do depend somewhat on hydrostatic mechanisms. Given that spiders, like worms, have a partial hydrostatic skeleton I am not sure that there is any difference in efficiency unless you say that the success of insects vs spiders shows that the insect design is more successful. I would say that the variety of motion shown by insects is an indication of the benefits of the opposing-muscle approach to design. Insects have established several mechanisms of flight while spiders have only been able to do it by parachuting. Perhaps this is an indication of the limits of a hydrostatic skeleton. I am not sure that it says anything about the efficiency of comparable motion in a biophysical sense. When a hydraulic system is more efficient, the insect uses it. The spider is limited to using blood pressure to extend limbs, perhaps because they have not developed an easy local
