A Giant Serpent of the Prairies? A Bull That’s No Bull!

A few years ago, driving along a back road in Parker County, a long, uneven dark line came into view on the pale caliche road. I pulled up closer on a four-foot snake stretched out in its sunset wanderings, nervously eyeing the human that was walking up to it. The bullsnake flattened its neck and tongue-flicked to check whatever scent it could pick up in the air, but tolerated my approach. There was a big scar along the right side of its face, probably the result of a near-fatal encounter with a predator or maybe a human. For a few moments it warily put up with my crouching beside it and I admired its allowing me to be there despite the glowering, don’t-tread-on-me expression on its face. And then, it was time for it to move on into the grasses and wildflowers, making its way along to wherever it was going. This was a treasured encounter in which the snake made no panicked attempt at escape or big defensive display, and I sought only to share a moment with the snake, without trying to collect it or harm it. I could almost make the case for it being marked by mutual respect, though the bullsnake probably just regarded it as a near-miss with something that could hurt it.

The bullsnake is one of our largest nonvenomous snakes, routinely growing to four or five feet in length. The record length is nearly nine feet long (Werler & Dixon, 2000). It is not so slender as a coachwhip, but smaller in girth than the western diamond-backed rattlesnake. The bullsnake has a pattern of dark blotches on a lighter sandy or tan background, with the darker blotches becoming more ring-like toward the tail. Its head is not as flat as is the case with other larger snakes such as the ratsnakes, and the snout is vertically flattened a little. At the tip of the snout, the rostral scale is taller than it is wide, and is somewhat raised from the surrounding scales. The structure of the underlying skull is more rigid than that of most snakes. Taken together, the head shape and skull rigidity enable the bullsnake to be very skilled at digging and excavating.

bullsnake-head

Bullsnake head, showing the vertically flattened snout and slightly raised rostral scale

bullsnake-juv-1

A young bullsnake, from Parker County

The bullsnake’s skills as an excavator were described by Carpenter (1982), who tested eight bullsnakes in an enclosure with sand substrate. The snakes generally began prodding the sand next to a stable object, and began digging sand with sideways movements of the head. Then, the snake bent its head to the side to scoop loosened sand and move it away. A loop of the neck continued to push the sand backward. In further testing, bullsnakes were seen to excavate tunnels up to a meter long. Additionally, Carpenter examined whether bullsnakes would recognize pocket gopher mounds, and showed that these snakes actively explore and excavate pocket gopher burrows in attempt to eat the gophers.

The diet of the bullsnake includes various rodent species, birds and their eggs, and the occasional lizard. Werler & Dixon (2000) reviewed literature suggesting that they may eat burrowing rodents such as gophers in greater numbers than species such as the hispid cotton rat that spend more time above ground.  Rodriguez-Robles (1998) examined published reports of stomach contents of Pituophis catenifer (including gophersnakes and bullsnakes), finding that mammals constituted 77% of prey items.

Their range in Texas includes central and west Texas with an eastern boundary that includes Lamar, Henderson, McClennan, Bastrop, and Victoria Counties (Dixon, 2013). That is, the eastern boundary of their range runs a little east of a line from Dallas down through Waco, Austin, and Corpus Christi. This means that the blackland prairie and parts of the adjacent post oak savannah serve as the eastern boundary of the bullsnake’s Texas range.  In west Texas, the bullsnake shades into the Sonoran gophersnake subspecies around the Pecos River. Bullsnakes occupy niches within the south Texas plains, the hill country, the cross timbers, rolling plains, and high plains. They make use of open habitats such as prairies and plains, but can also be found in rocky hillsides and bluffs in the hill country. A study of bullsnakes in Wisconsin found that the snakes preferred south-facing open canopy bluffs but mostly avoided agricultural lands (Kapfer, et al., 2008). They examined the relationship between amount of preferred habitat and home range size, and concluded that where there are large patches of good habitat, bullsnakes can live within smaller home ranges. Where preferred habitat (such as grassland and savannah) is broken up by farmland and other less-usable land, they travel over larger areas and do not survive as well. Werler & Dixon (2000) noted that researchers in Nebraska reported bullsnake home range sizes of 10 to 42.5 acres.

Predators of bullsnakes undoubtedly include birds of prey such as the red-tailed hawk, as well as coyotes and other medium-sized carnivores. It seems very likely that people are a significant source of bullsnake mortality. Because they are large snakes that are sometimes active during the day and frequently cross roads, they are more easily seen and targeted by humans who may kill them or run over them in cars. Additionally, the slight resemblance of bullsnakes to rattlesnakes undoubtedly increases the number of deaths at the hands of humans. Bullsnakes have a very intimidating threat display when cornered or caught, raising the head and first part of the body in preparation for striking, hissing loudly, and vibrating the tail. The hissing has been described as like the sound of escaping steam, and it shares a little similarity to the high-pitched buzz of an enraged rattlesnake. The particular sound quality is the result of a small band of tissue (the epiglottis) positioned vertically just at the opening of the airway (the glottis). When air is forced around it, a loud hissing sound is created. A large bullsnake that is aroused in such a way gives the impression that it could be quite dangerous, although it is not. Instead of frightening the person away, it’s likely that this behavior often leads to the snake being killed.

MS-Pituophis-catenifer-sayi9-Menard

The glottis is the opening just behind the tongue, and the epiglottis is the vertical strip of tissue just in front of it

Many of us, at least in north central Texas, would report seeing fewer bullsnakes than we used to. Decades ago, I remember finding them much more often, but the cities were smaller then and there was more prairie and ranchland around the edges of Fort Worth. However, bullsnakes are not considered to be imperiled overall. The International Union for the Conservation of Nature (IUCN) notes that the bullsnake has not yet been assessed for the Red List of Threatened Species. It is not listed in the Species of Greatest Conservation Need compiled by Texas Parks & Wildlife Department. Overall, the status of the bullsnake in Texas has not been identified as a concern, but like many other species of herpetofauna, we may not know just how secure it is. I hope that bullsnakes continue to live in healthy populations wherever there is enough good prairie and savannah habitat. When I think of the prairie out west of Fort Worth, the image of the bullsnake comes to mind along with images of grasses and forbs, pale yellow yucca blooms, little massasauga rattlesnakes, and the beautiful calls of doves and chuck-will’s-widows in the evenings. It is a wonderful, shrinking ecosystem, and I hope we save it in places here and there. And it would not be the same without the bullsnake.

Carpenter, C.C. 1982. The bullsnake as an excavator. Journal of Herpetology, 16(4), Pp. 394-401.

Dixon, J.R. 2013. Amphibians and Reptiles of Texas (3rd Ed.) College Station: Texas A&M University Press.

IUCN Red List of Threatened Species (Internet). http://www.iucnredlist.org/search (accessed 2/12/17)

Kapfer, J.M., J.R. Coggins and R. Hay. 2008. Spatial ecology and habitat selection of bullsnakes (Pituophis catenifer sayi) at the northern periphery of their geographic range. Copeia 2008(4), Pp. 815-826.

Rodriguez-Robles, J.A. 1998. Alternative perspectives on the diet of gopher snakes (Pituophis catenifer, Colubridae): Literature records versus stomach contents of wild and museum specimens. Copeia, 1998(2), Pp. 463-466.

Texas Parks & Wildlife Department. Texas Conservation Action Plan: Species of Greatest Conservation Need.  http://tpwd.texas.gov/landwater/land/tcap/sgcn.phtml  (accessed 2/12/17)

Werler, J.E., and J.R. Dixon. 2000. Texas Snakes: Identification, Distribution, and Natural History. Austin: University of Texas Press.

5 thoughts on “A Giant Serpent of the Prairies? A Bull That’s No Bull!

  1. Splendid article my friend! A real dose of pain killer that doctors can’t prescribe as I’m lying here hobbled up! A few interesting personal notes on bull snakes, if I may…

    1) I once owned a bull snake when I was a kid that would eat road-killed snakes with relish (not the condiment, the suggestion that it would readily accept them)

    2) the strangest “habitat” I ever found one in was in south Fort Worth city limits on a woman’s front doorstep in a subdivision with well-manicured lawns of St. Augustine (don’t ask what either of us were doing there…)

    3) in the wonderful depiction of bullsnake defensive posture in the pic showing the glottis/epiglottis if you zoom in on the snake’s eye you can see a splendid blue sky with clouds and a treeline
    Love bullsnakes and loved the article!

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  2. Bullsnakes are one of the more personable and entertaining of snakes. One small correction: the epiglottis is actually the upper flap that closes off the glottis during swallowing in many vertebrates. The vertical flap of bullsnakes is an unrelated adaptation for the hissing defensive display and presumably makes the hissing louder (or prevents them from blowing up the glottis since they blow pretty hard). To my knowledge, only Pituophis has this flap, though many snakes have hissing displays. Other species may have the feature, but I don’t know of any.

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    • Interesting – I’ve seen numerous references to the “epiglottis” as the vertical structure immediately in front of the glottis in Pituophis, but I suppose the description of what it is and how it works is the main thing. Like you, I’m not aware of other snake species having this particular adaptation.

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