Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 30, Number 6;   June, 2003

The Texas Rat Snake (Elaphe obsoleta lindheimeri)

by Michael Smith

The Texas rat snake may be the subject of more run-ins with people than any other species in our area. Lots of "snake calls" are generated by people seeing Texas rat snakes in their trees or yards. Lots of Texas rat snakes are killed on the road each year. Somehow these animals continue to be abundant year after year around parks and suburbs, despite being killed (and relocated by well-meaning herpers) in fairly large numbers. With a variable and indistinct pattern, these snakes are described in widely differing ways by excited or scared people trying to get help in identifying them. Someone who has seen one of these snakes may describe it as green, red, striped, blotched, or any number of colors and patterns.

Description
This is one of our longest snakes, with Tennant & Bartlett (2000) as well as Werler & Dixon agreeing on the average length being 3.5 to 6 feet, with a record length of seven feet. Like several other rat snake species, the Texas rat snake is somewhat angular in cross section - that is, if you were to cut it in half, the cross section would be rounded on top and square at the belly, shaped like a loaf of bread. This physical attribute is thought to aid the snake in climbing trees.

The fairly broad, flat head is dark gray on top (in adults) shading to white on the lips and chin. Starting with the neck, there is a pattern of dark saddles going down the back. The ground color may be yellowish-gray to gray. (Werler & Dixon say that the ground color is more yellow in the western open woodlands and more gray in the eastern, more forested part of the range.) Along the sides is another row of blotches, these being somewhat diamond-shaped. The ground color may be mottled or may tend to form vague dark stripes down the back. Further, the skin between the scales may be reddish or orange, especially around the neck, and on the dark blotches there may be some white or light gray skin inside each blotch.

On the belly, the scales are light on the throat, darkening from front to back with pale squarish blotches and then a mottling of gray and yellowish toward the tail.

The overall result of this complicated pattern is a snake that can vary from nearly black to somewhat gray or yellow or orange-tinged, with indistinct blotches and possibly a suggestion of vague stripes as well.

And then there are the hatchlings. These little snakes emerge from eggs each fall and show up in the darndest places, where they are mistaken for everything from pythons to rattlesnakes. The hatchlings have a much lighter ground color than the adults, and the blotches stand out distinctly. On the top of the head there are some dark flecks and a broad, dark band across the snout. That band goes through the eyes and diagonally down to the jaw. As the snakes mature, the pattern darkens.

Taxonomy
For many years the rat snakes in the eastern U.S. have been divided roughly into the black rat snake group (including black, yellow, gray, Everglades, and Texas subspecies), the corn snake group and the fox snakes. Some recent studies have proposed that the black rat snake group, rather than being several subspecies of Elaphe obsoleta are really three distinct species. East of the Allegheny Mountains, these snakes would be Elaphe alleghaniensis, the "eastern rat snake." West of the Apalachicola River and east of the Mississippi, they would be Elaphe spiloides, the "midland rat snake" (largely represented by what we have known as the gray rat snake). West of the Mississippi these snakes would be Elaphe obsoleta (no subspecies), the "western rat snake." The fact that all three species tend toward being plain black or dark brown in the northeastern parts of their ranges is said to reflect: either a tendency among all three to have evolved darker patterns in the colder parts of their ranges - to better soak up heat - or a common ancestry.

Will the "Texas rat snake" become a historical note, with future herpers talking about western rat snakes and puzzling over the old-timers still sometimes referring to "Texas rats" or "lindheimers?" Time will tell. The classification of organisms is constantly evolving, and changes become accepted when most scientists agree that the change is valid.

Habitat
These snakes take advantage of a wide variety of habitats, from woodlands to prairies and open fields. They are more likely to be found in areas with trees, or at least savannahs (grasslands with scattered trees) or mottes (clumps of trees in grassland areas). The Texas rat snake is an excellent climber, and this may be one factor in its success, keeping it away from ground-based predators. These snakes also eat birds and their eggs, so spending time in trees functions not only to keep them away from some predators, but also helps them to find their food.

Texas rat snakes range through the eastern half (or two-thirds) of Texas and east through parts of Louisiana.

My field notes reflect lots of Texas rat snakes found in prairie and old field habitats with at least small creeks nearby, providing brushy cover. During the day, I've been more likely to find them while flipping cover such as discarded plywood or deadfalls of wood. I've seen a great many on the roads at twilight or at night, quite often in brushy or wooded areas, or within a short distance from a creek. At the Dallas Zoo they are seen in the trees or around exhibits, sometimes giving zoo visitors considerable excitement. Zoo staff have hypothesized that they use creek corridors to come from Trinity River habitat into the zoo grounds.

Food
Both the accepted common name ("rat" snake) and a name commonly given to it ("chicken" snake) refer to its preferred food. The Texas rat snake devours many rats and mice - a stomach contents study cited in Werler & Dixon, looking at 100 wild specimens in north Louisiana, found mice and rats - as well as a few squirrels and rabbits, in their stomachs. The snake kills its prey by constriction.

When birds are available, this snake is more than happy to eat them and their eggs. Coming upon nests, the snake may eat eggs or fledglings that are confined to the nest. It can also eat adult birds, and a big adult reportedly can swallow an adult chicken. While this will not make the Texas rat snake popular with either farmers or birders, it is simply doing its "job" and may eat enough rats that it does the farmer more good than harm.

Activity
The most memorable activity seen in Texas rat snakes is their belligerent self-defense. When first approached, the snake may "make a break for it" or it may stay where it is. I have often seen one on the road pull its body into a series of short kinks and sit still until it has been picked up. Once touched or cornered, the typical Texas rat snake behavior is to bite repeatedly and discharge a particularly foul musk. While water snake and garter snake musk is moderately disagreeable, the musk from a Texas ratsnake is very offensive and a little reminiscent of burnt tires.

This is a subspecies that is famous for its bad attitude when picked up. A behavior that furthers its bad reputation is its open-mouthed gapes as it watches for a target. Very commonly, having picked up a Texas rat snake, it remains coiled on your one arm as if it were a tree limb, while gaping at your other arm as the only visible target. If the hand moves closer, the snake will strike, leaving a series of pin-prick holes. Occasionally it will hold on and chew. Once, years ago, I uncovered a Texas rat snake in the field and picked it up, and it promptly bit my thumb. It began to chew, and as I did not struggle (pulling away makes it worse) the snake transitioned from defensive biting to swallowing, and swallowed my thumb up to the hand. With other Texas rat snakes, I have often been lulled into thinking that this specimen may be more calm, and may be the one to keep at home. This happens because once in the hand and properly supported with only minimal restraint and nothing triggering a defensive reaction, the snake may move about calmly and without Biting. However, once I put the calm, non-biting snake down, I am no longer simply the tree upon which it is climbing and I then become, to the snake, an aggressor. Bring on the band-aids!

If you know people who don't want to encounter Texas rat snakes and are a little fearful when they do, it is well to let them know that these fearsome snakes have only small, needle-sharp teeth and cannot really do any harm. For the average person it could be frightening to be bitten by a big one, but they usually bite and let go, and might not be able to bite through a flannel shirt. They don't bite unless cornered or picked up.

Depending on the time of year, this snake's activity may be primarily during the day or at night. Much of the time it is a day-active snake, but with hotter weather it is found most often at night. In late spring and summer months I have often found them on the road at sundown or within the first couple of hours after sundown.

Abundance
This is a very successful snake, continuing to be abundant in areas away from towns as well as in farm areas and areas within cities where nearby creek or river corridors provide belts of trees and some shelter. It may be that its arboreal habits are partly responsible for its being able to live so close to people. There do not appear to be field studies documenting its population status, and so we don't know for sure, but the number of sightings each year leaves little doubt that the Texas rat snake is doing well.

Reproduction
Spring matings result in the laying of clutches of eggs in June or July. Werler & Dixon indicate that the clutch size is from 5 to 20 eggs. The eggs are laid in rotting logs, leaf litter, or in mammal burrows or under rocks. This snake is known to use above-ground tree cavities for nesting, and the description in Werler & Dixon notes that the tree cavity was used by perhaps four different females for communal nesting.

The young hatch in August and September, and the little snakes have much the same temperament as their parents.

Notes
These are often attractive snakes that can do quite well in captivity, readily eating rodents. The tendency to remain defensive, gaping and striking even after a considerable time in captivity, discourages many people from keeping wild ones. A leucistic form (pure white with dark eyes) is available in the pet trade.

References & Additional Reading
Tennant, A., and R.D. Bartlett. 2000. Snakes of North America: Eastern and Central Regions. Gulf Publishing Co., Houston.
Werler, J.E., and J.R. Dixon. 2000. Texas snakes: Identification, Distribution, and Natural History. University of Texas Press, Austin.