On the face of it, one might logically assume that a snake is one of the least adaptable and most likely unsuccessful creatures on the planet. A snake is nearly deaf. It can’t chew its food. Without limbs, its locomotion is limited, and it can’t stand extreme heat or cold. However, such conclusions would be dead wrong.
The Diversity and Distribution of Snakes
Surprisingly, you find the approximately 2,900 species of these legless reptiles virtually everywhere in deserts, grasslands, forests, mountains, and even oceans around the world; everywhere except the Arctic, Antarctic, Iceland, Greenland, Ireland, New Zealand, and some small oceanic islands.
It is far too cold for snakes to live in the Arctic, Antarctic, Iceland, and Greenland. New Zealand has no snakes because continental drift carved it off from Australia and Asia before snakes ever evolved there. New Zealand is now surrounded by water and snakes simply cannot get there. (As far as can be determined, no snake has successfully migrated across the open ocean to a new terrestrial home.) As the world’s ocean levels have risen and fallen over the millennia, land bridges have come and gone between Ireland, other parts of Great Britain, and the European mainland.
However, any snake that may have slithered over those land bridges to Ireland would have turned to an ice cube by the glaciers that advanced and retreated across Ireland more than 20 times. Ireland thawed out for the last time only 15,000 years ago. Since then 12 miles of icy-cold water in the North Channel have separated Ireland from neighboring Scotland, which does harbor a few species of snakes.
Most snakes are colored in drab browns, grays, or black. Some have bright red, yellow, or vivid green marking in arrangements from blotches to rings, cross bands, and stripes. Snakes cannot change color to any great degree the way many lizards can.
The smallest snake is the tiny burrowing thread snake (Leptotypholps) only 15 cm (6 inches) long and no bigger around than a matchstick. However, there is much debate about the largest snake in the world. The reticulated python (Python reticulatus) of Southeast Asia and the East Indies can reach 8.4 m (27.6 feet) in length, but the South American anacondas may rival or surpass that.
For decades persistent but unsubstantiated reports have been made of 11-45 m (33.5-148 feet) long anacondas. The average size of an anaconda is around 4.5 m (15 feet) and while some undoubtedly grow much larger, most herpetologists believe that a 15-18 m (50-60 feet) anaconda strains credibility and that a 45 m (150 feet) long one is an outright impossibility.
It should be noted that since the early 20th century the Wildlife Conservation Society has offered a large cash award (currently worth US $50,000) for live delivery of any snake 30 feet or more in length. The prize has never been claimed.
The Body Plan of a Snake
An elongate and limbless body requires a number of modifications to the standard vertebrate plan. The skeleton of a snake may contain more than two hundred vertebrae and pairs of ribs. Joints between the vertebrae make the body very flexible. Narrowing of the body has also resulted in the reduction or loss of the left lung and the displacement of the gallbladder, the right kidney, and often the gonads into a single file arrangement like the cars of a train.
Skull adaptations facilitate swallowing large prey. The upper jaws are movable on the skull and the upper and lower jaws are loosely joined so that each half of the jaw can move independently.
In addition, the two halves of the lower jaw (mandibles) are joined only by muscles and skin, not rigid bone. Such flexibility allows a snake to open and spread its mouth and flex its highly kinetic skull in order to swallow prey that may be considerably larger than itself.
Furthermore, snakes have a swallowing snorkel known as a glottis. The glottis is a tube-like tracheal opening the snake extends to allow it to breathe while swallowing.
Reputedly, the biggest prey on record is a 59 kg (130-pound) antelope that was swallowed by an African rock python (Python sebae). And while no dispassionate biologists have ever actually observed it under controlled laboratory conditions, there are numerous accounts of snakes interrupted in the act of swallowing a person, or found with a big bulge that once slit open, yielded a human being.
Whether you love them or loathe them, one should snakes should be respected and admired for their ecological success in spite of their physical shortcomings.
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