Texas Field Notes - Great Plains Rat Snake (Elaphe emoryi)

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Texas Field Notes

The Great Plains Rat Snake (Elaphe emoryi)

This is one of our more inoffensive and subtly pretty snakes. They aren't dramatically colorful but they're "handsome," and their big eyes give them a sort of engaging face.

Unfortunately many of the Great Plains rat snakes I see are DOR, or "dead on road," in field herping jargon. A sampling from my field notes shows that I've seen these snakes in north Texas, central Texas and the Hill Country, and the Trans-Pecos, mostly in April and May but a couple in June and also in August and September. I've found them anywhere from about 9:00pm to just after midnight. And, on the roads, most have been DOR. One evening in August 2002, at 8:40pm, just as it was getting dark, the Benbrook-Aledo Road yielded up one more Great Plains rat snake. I had passed an oncoming pickup truck a half-mile back, and then I came upon this small snake slowly moving across the road. When I picked it up, I thought about how long it had been since I'd seen one alive on the road, and then I noticed that its struggles were not well-coordinated and it had a tinge of blood under the right eye cap. I took it along to see if the injuries would prove to be fatal; if it died, at least it could add to the scientific collection at UTA. The snake did not die, and is pictured in this article.

Relationship to other species
Herpetologists have come to various conclusions about how this snake is related to others. For a long time it was considered a subspecies of the corn snake and given the name Elaphe guttata emoryi. Recently it was proposed that the south Texas specimens were a separate species, E. g. meahllmorum, and were referred to as "southwestern rat snakes," but this has not been completely accepted. Several researchers have concluded that this snake is a full species, not a subspecies of corn snake. This point of view seems to be gaining acceptance. The list of accepted names from both the Society for Study of Amphibians & Reptiles and the Center for North American Herpetology currently opt for the name Elaphe emoryi.

In Wright & Wright's Handbook of snakes, the common name at the time was "Emory's pilot snake" or "Emory's rat snake" (still in some use today). Other common names included "Spotted mouse snake." And at that time, this snake was given species status: Elaphe emoryi. What was old is new again.

Description
It is not surprising that this was considered a subspecies of corn snake, because at first glance it looks like a gray-brown corn snake, with a similar shape and similar pattern of blotches down the back. Several other prairie and woodland snakes are brown-blotched, such as the prairie kingsnake. Among the most important distinguishing marks of the Great Plains rat snake is the "spear point" pattern on the top of the head. Viewed from the top, this snake (and the corn snake) has two dark markings that come together on the crown of the head, pointing forward. There is also a dark band across the snout that angles back through the eye to the corner of the mouth.

The dorsal blotches may be a bit longer on north Texas specimens, while E. emoryi in west Texas may have more narrow blotches and the snake may be somewhat paler. Those blotches, down the body and tail, average 67 more than those of the corn snake. Blotches may be a rich brown or may be more gray or slightly olive-colored.

Underneath, The Great Plains rat snake has a white belly with black markings, but they tend not to be as bold as the black checkerboard of the corn snakes belly. Under the tail, the dark markings fuse into two stripes toward the end, just like the corn snake. Scales are weakly keeled, and the anal plate is divided. This helps differentiate it from the similarly-marked prairie kingsnake which has smooth scales, a single anal plate, and relatively smaller eyes and head than the Great Plains rat snake. Young Texas rat snakes have a band across the snout and a somewhat similar blotched appearance, but they do not have the spearpoint design on the head or the stripes underneath the tail.

Great Plains rat snakes tend to be about 24 to 48 inches long. Werler & Dixon (2000) show the record length as 72 inches, while Tennant (1998) shows it to be just over 60 inches.

Habitat
This is a snake that can live in a variety of habitats, from prairie and open woodland to rocky hillsides and even caves (where it reportedly feeds on Mexican free-tailed bats). In our area I have most often seen them in remnant or disturbed prairie or old fields near barns and discarded materials that provide ground cover. Ecologist Jim Eidson, at the Nature Conservancys Clymer Meadow in north Texas, cites it as a common species there. Herpers commonly find Great Plains rat snakes while herping the Trans Pecos and Big Bend, and they are found throughout the hill country.

From Texas, the range of the Great Plains rat snake extends down into Mexico, westward into New Mexico, up through Oklahoma and much of Kansas, and into parts of Missouri and Arkansas. It is also found in a disjunct area of western Colorado and adjacent Utah.

Food
Mice and rats appear to be the primary prey items, but these snakes will also take ground-nesting birds and their young. As noted above, these snakes will eat bats, and they have been reported living inside caves where they helped themselves to the free-tailed bats found there. In captivity, these snakes do well on a rodent diet just as one would feed a corn snake.

Activity and Behavior
Depending on the local climate, Great Plains rat snakes may emerge from hibernation by March. At the end of their activity season, they may enter burrows, crevices or caves for hibernation by October or November (again depending on local temperatures). They are active at night, and tend to be secretive. Thus, they are found either by turning boards, rocks, or other ground cover, or by road-cruising at night. When discovered, they may rattle their tails and might offer to bite if picked up. However, it is very common for a Great Plains rat snake not to bite, even when initially picked up in the wild. In captivity they have an easygoing temperament similar to the corn snake.

Abundance
Field notes and observations of naturalists and field herpers indicate that this is a common snake. In places it is not encountered as often as the less-secretive snakes, but in suitable habitat areas it is generally considered abundant.

Reproduction
Mating occurs soon after leaving hibernation, and females deposit from 3 to 27 eggs (Werler & Dixon, 2000) in June or July. The Great Plains rat snakes eggs are coated with an adhesive substance that tends to lock the eggs together in an inseparable mass. The approximately 10 to 15 inch babies hatch in August and September.

References and Additional Reading:
Conant, R., & J. T. Collins. 1998. A field guide to reptiles and amphibians, eastern and central North America (3rd Ed.) Boston, MA: Houghton Mifflin.

Crother, B.I. (Committee Chair) 2000. Scientific and standard English names of amphibians & reptiles of North America north of Mexico, with comments regarding confidence in our understanding. Society for Study of Amphibians & Reptiles. Online: http://www.herplit.com/SSAR/circulars/HC29/Crother.html

Tennant, A. 1998. A field guide to Texas snakes (2nd Ed.) Houston, TX: Gulf Publishing.

Werler, J., & J. R. Dixon. 2000. Texas snakes: Identification, distribution, and natural history. Austin, TX: University of Texas Press.

Wright, A. H., & A. A. Wright 1957. Handbook of snakes of the United States and Canada. Ithaca, NY: Comstock.

(Article by Michael Smith. A version of this article was published in the September, 2002 issue of the Cross Timbers Herpetologist, newsletter of the Dallas-Fort Worth Herpetological Society. See www.dfwherp.org)