A mantis shrimp escapes by somersaulting backwards like a wheel
Nannosquilla decemspinosa curls into a living wheel and rolls away at 72 rpm, covering more than 2 m. Animals also sail, kite on silk, skate on surface tension and hitch rides on other creatures, and flying fish beat their tails up to 70 times a second to take off.
Zoologists count running, swimming, jumping, hopping, flying, soaring and gliding as self-propelled movement, but many species let the environment carry them: some jellyfish sail, spiders kite on silk, certain beetles and spiders roll, and some creatures ride on others, a habit called phoresis. Animals travel to find food, mates and good microhabitats or to escape predators, so natural selection shapes how they do it. Long-distance migrants such as the Arctic tern tend to use methods that cost little energy per kilometre, while prey that must bolt often rely on fast but expensive bursts.
Water is far draggier than air, so body shape matters, and many swimmers share a torpedo-like outline. Most fish drive themselves with side-to-side body waves ending in a big tail fin, while marine mammals flex up and down. Rays, skates and the spotted ratfish row with their pectoral fins, seahorses move without body waves at all, penguins and diving ducks practise aquatic flying, and cephalopods suck in water and blast it out as a jet. Dolphins sometimes surf the bow waves of boats.
On the seabed, echinoderms creep on tube feet tipped with suction pads, helped by sticky mucus. Crabs usually walk sideways because their leg joints make that gait efficient, though a few walk forwards, and swimming crabs have their last legs flattened into paddles. Velella, the by-the-wind sailor, cannot propel itself except with a small rigid sail that sends it downwind at a slight angle. Water striders stand on the surface film with water-repellent legs, whereas the basilisk lizard breaks through it as it runs.
Flight is a fight with gravity, since no animal can be as light as air; wings must generate lift, and the heaviest living fliers are birds of about 20 kg. Gliding, travelling further horizontally than it drops without thrust, has evolved more often than powered flight, appearing in gliding ants and flying snakes. Flying fish usually glide about 50 m but can stretch to 400 m on updrafts off wave crests, and some squid keep jetting water after leaping into the air.
Source: Animal locomotion
