A Western Ribbon Snake in Santa Fe, Texas 2

—This article by Jerry Cates and Tammy D., first published in December 2009, was last revised on 6 July 2012. © Bugsinthenews Vol. 10:12(01).

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Western Ribbon snake (Thamnophis proximus proximus), Tammy D Santa Fe TX 122209 Body

Tammy wrote: Hello Jerry–I found this snake under some leaves in my yard in Santa Fe, Texas. Can you tell me what kind it is. Thank you — Tammy

My thanks to Tammy for these excellent photographs. They are at high resolution, so it is possible to work with them to bring out important but subtle features.  Click on each photo to enlarge them for viewing.

The city of Santa Fe is in Galveston County, near, but inland from, the Gulf Coast.

A fairly large number of snake species native to North America display well-defined longitudinal stripes that are not mixed together with other primary markings such as blotches, saddles, or the like. If one of these is a spinal stripe (thus excluding Baird’s rat snake and all the whip snakes, which are striped, but not on their spines), and that stripe is narrow (thus excluding the mountain patch-nosed snake, which has a broad spinal stripe) and brightly colored (thus excluding the Texas patch-nosed snake, which has a narrow spinal stripe that does not contrast brightly with the snake’s background color) in comparison to the background coloration of the snake–as in this specimen–the field of possibilities narrows considerably.

With few exceptions–e.g., the lined snake (Tropidoclonion lineatum)– that field embraces a single genus (Thamnophis), which comprises a long list of garter and ribbon snakes.

Western Ribbon Snake (Thamnophis proximus proximus); Tammy D Santa Fe TX 122209–Midbody Scalation

The scales of  members of the genus Thamnophis are keeled, i.e., they possess a ridge that runs longitudinally through the center of each scale, vs. a smooth scale that does not have such a ridge.  This specimen’s scales are remarkably keeled. The number of  midbody scales of snakes in this genus are usually 19, but sometimes total 21.

If you click on the photo at left, the enlarged image has been annotated to show the number of dorsal scales from belly to spine. These number 10 for this specimen, including the spinal scale.

Inasmuch as most species of snakes have an odd number of dorsal scales, and the spinal scale on this specimen is at the precise center of the spinal stripe, we can assert with confidence that another nine scales will complete the trip to the belly on the far side that is not visible in the photo. Thus, this specimen has a total of 19 dorsal scales.

Western Ribbon Snake (Thamnophis proximus proximus); Tammy D Santa Fe TX 122209 Right Frontal Head and Body

The scales on the crown of the head are easily distinguished in Tammy’s photograph at left. Note the two small yellow dots foward of the larger yellow spot on the crown of this specimen. These are common markings on ribbon and garter snakes, though it is not unusual for the two smaller dots to be joined together.

Notice the large eye, with a round, dark pupil. These two features, together, mark this–at least in North America–as a “non-venomous” snake. None of our vipers have round pupils; their pupils are like those of  a cat, instead. Our Elapid coral snakes have round pupils, but their eyes are extremely small, and are surrounded by black scales that make it hard to see the eyes at all.

That is quite unlike our specimen here, whose large eyes and large pupils are immediately noticeable. One reason the eyes are so noticeable is that a bright, pale pre-ocular scale lies forward of and immediately adjacent to the eye, while two bright, pale post-ocular scales lie just behind and also immediately adjacent to the eye. The bright pale pre-ocular scales  markings are present in all members of the genus Thamnophis, but only the Western black-necked garter (T. cyrtopsis cyrtopsis) and the western ribbon snake (T. proximus proximus) have two such postocular scales consistently, where both scales are equally bright in coloration.

Western Ribbon Snake (Thamnophis proximus proximus); Tammy D Santa Fe TX 122209–Left Lateral Head

You may wonder how one distinguishes between the garters and the ribbons. Both hail from the same genus, so how are they different? Two bodily features, one anatomical, the other by way of coloration, separate the two groups.

Look at the first photo on this page, and notice that the body is slender along its entire length, and that the tail is extremely long. In the ribbon snakes, the tail is a full one third of the snake’s length, while in the garters, whose bodies are relatively stocky, the tail is much shorter, and never occupies more than a quarter of the body’s total length.

Now examine the photo at left, paying particular attention to the labial (lip) scales on this specimen’s face. Garter snakes display dark margins on most, if not all the upper labials, while those of ribbon snakes are immaculate–to the point that none of the labial scales have dark margins of any kind, as with this specimen.

All snakes in the genus Thamnophis are considered “warm” herps, in that their saliva contains a mildly neurotoxic substance that is used to subdue their prey.  Garters have sufficiently large mouths, and pugnacious attitudes to boot, which together may produce non-trivial bite wounds when handled in the wild or, with domesticated specimens, roughly under any circumstances. Ribbon snakes, on the other hand, have such small mouths and teeth that, even if they were aggressive biters–which they are not–the resulting wound would be inconsequential, their mildly toxic saliva notwithstanding.

The snakes in the genus Thamnophis are all either beneficial or neutral. They should be protected for their predation on anurans and toads, which aids in keeping such populations in check. Though their saliva is slightly toxic, it does not appear to pose a serious hazard to humans or their large pets. It is questionable if these snakes should be handled by children, however.