Some animals move across both land and water with similar, flowing motions. This dual locomotion, characterized by slithering on solid ground and effective swimming in aquatic spaces, allows these animals to thrive in diverse habitats. Understanding how they achieve this versatile movement reveals adaptations in their body structure and behavior.
Creatures of Land and Water
Many animals slither and swim, with snakes being a prominent example. Various species, from common garter snakes to large anacondas, readily move through both terrestrial and aquatic environments. Sea snakes, like the pelagic sea snake, spend almost their entire lives in marine waters, possessing flattened, paddle-like tails for swimming, yet can maneuver on land if necessary.
Beyond snakes, other limbless or elongated creatures also demonstrate this dual movement. Eels, including snake eels and American eels, are known for their aquatic lives but can slither over land for short distances to find new water sources or prey. Amphibians like some salamanders and caecilians, limbless amphibians resembling large worms, navigate both damp terrestrial and aquatic environments using similar undulating body movements.
How They Move
The principle behind both slithering and swimming in these animals is lateral undulation. This involves S-shaped curves that ripple down the body from head to tail. As the animal slithers on land, these curves push against ground irregularities, creating friction that propels the body forward. Specialized scales on their bellies provide frictional anisotropy, offering more grip in one direction than another, aiding forward propulsion while resisting backward sliding.
In water, the same lateral undulation is employed; instead of pushing against solid objects, their body waves push against the water. Water resistance allows the undulating body to generate thrust, moving the animal through the liquid. While the basic mechanism is shared, subtle differences in muscle activity and body flexion timing optimize movement in each environment.
Why Live a Double Life?
The capacity to both slither and swim offers advantages, allowing these animals to exploit a broader range of resources. They can access food sources in both terrestrial and aquatic habitats, such as small mammals or amphibians on land, and fish or crustaceans in water. This versatility increases their dietary options and overall foraging success.
Moving between land and water also provides strategies for escaping predators. An animal pursued on land can retreat into water, and vice versa, using the change in environment to evade capture. This adaptability also helps them find shelter, locate mates, or disperse to new territories, enhancing their survival and reproductive opportunities across varied landscapes.