Eating Habits of Reptiles (Part 2)

A similar progression from insect diet to some specialized sort of feeding is to seen in various kinds of snakes, which as a group are the most elaborately specialized feeders among the reptiles. Here, however, the change is not eating to whatever restricted food the adults may specialize in. The rat snakes of the genus Elaphe, for instance, when grown show strong preference for warm-blooded prey and for eggs, but very young rat snakes eat nearly any living thing that they can catch and swallow. During their earliest weeks of life this means insects; later on frogs are added to the list, and when finally an adequate body size is reached, the adult diet of mice, birds and eggs becomes practicable. In all these cases the progression of feeding habits is clearly dictated by the relative availability of food that the animal is able to take in.

It is their leglessness that most obviously sets the snakes apart from the lizards, their fellows in the order Squamata. Actually, however, feeding adaptations were also behind the initial evolutionary separation-and these are fully as striking as their lack of legs. The whole structure of a snake’s head and jaws, for instance, is designed to provide the stretch that allows it to take in creatures bigger around than itself. This ability obviously gives snakes greater scope in their feeding outlook and, indeed, most adult snakes will either eat anything live that they can swallow or show some kind of curiously specialized food preference, like Dasypeltis, and African genus which eats only eggs. It might even be said that the gape of the snake made the snake plan feasible. In any case, of all the many ventures into limblessness which the Squamata have made, the only one that prospered markedly was the one that accompanied this extraordinary ability to accommodate oversized food.

Most lizards, on the other hand, have continued in the traditional insect-eating role. Though some among them will occasionally pick up small pieces of bread or bits of fruit thrown to them, eating pieces of objects rather that whole objects is really out of character for Squamata.

In eating very small prey, lizards simply grab and swallow, but when they feed on larger animals they employ a swallowing technique called inertial feeding. Objects too big to be taken in immediately are seized and then engulfed by a process involving a sudden relaxing of the jaw-hold, followed by a quick sideways thrust that moves the jaw forward. The inertia of the object gives the advancing jaws something to push against. The lizards carry out the process by moving first one side of the jaw forward and then the other indicates the far more specialized “jaw-walking” method of swallowing carried out by snakes.

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