Background for Teachers
TPW Magazine, August 2009
Do snakes fascinate you or strike fear in you? Seems like people have strong opinions but one thing is for sure, snakes play a critical role in our ecology.
There are around 2,600 species of snakes worldwide. Snakes are found on every continent except Antarctica. Here in Texas, we have 76 species of snakes. The Brazos and Concho water snakes (Nerodia harteri) are found nowhere else but Texas.
Snakes appeared on Earth about 60 million years. They are the descendents of ancient lizards that abandoned life on the surface and began to live underground (fossorial). During this time legs were reduced in size and then finally lost altogether. Mobile eye lids were replaced by a clear scale called a brille and external ear openings closed, rendering snakes deaf.
Most snakes do not see very well, but have developed other means of finding food and avoiding enemies. They have a forked tongue that they use to collect molecules from the air and the ground. When the tongue is retracted it is placed in a specialized portion of the roof of the mouth called the Jacobson's organ. Western diamondback rattlesnakes (Crotalus atrox) often extend their tongues for prolonged periods if they detect a potential predator.
Snakes swallow their prey whole. The left jaw and the right jaw are not fused at the front like that of mammals. This allows them to stretch their mouths to accommodate large meals. Snakes' backward-pointing teeth make it difficult for prey to escape.
Prey ranges from earth worms and slugs, to spiders and scorpions, to fish and amphibians. Other items on the menu may include reptiles, even other snakes, birds and their eggs, and small mammals, depending on species. Some snakes have very specialized diets, such as crayfish snakes (Regina rigida), which eat only freshly molted crawfish. Others, like the Texas indigo snake (Drymarchon corais) eat a wide variety of prey.
Some snakes species, like the rough green snake (Opheodrys aestivus), simply over power their prey and often eat it alive. Rat snakes (Elaphe obsoleta) grasp prey in their mouths and quickly throw loops of their body around the prey, killing by constriction. Venomous snakes, such as copperheads (Agkistrodon contortrix), bite and inject venom in their prey. The copperhead does not risk injury to itself and the venom not kills the meal, but begins to break down the body digestively. Use of venom to defend itself is a secondary purpose.
Pit vipers have fangs in the front of their mouths that are hollow like hypodermic needles that inject venom. Coral snakes have a u-shaped fang in the rear of their mouth that allow venom to seep down into the puncture. Embryonic pit vipers fangs begin in the rear of the mouth and as the snake develops, migrate to the front of the mouth. This and other recent discoveries indicate that snakes evolved from a common ancestor.
Snakes help keep populations of hungry mice and rats in check, a crucial help to farmers. Just as importantly, snakes are a major food source for many birds and other species.