Wyoming Wildlife - August 2018

One Cryptic Constrictor

Dayton Game Warden Dustin Shorma holds a rubber boa he found not far from his home. In his 30-plus years afield with the Game and Fish and as an exploring youngster, he has spent considerable time outside, but this was his first encounter with a rubber boa.

Consider yourself lucky if you encounter this worm-like snake with an easy-going demeanor. It is one of the most uncommon reptiles in the Cowboy State.

Christina Schmidt Shorma
8/1/2018 10:02:55 AM

Paul-Émile Botta, a French-Italian scientist, embarked on a three-year voyage on the French trading ship Le Heros in April 1826, serving as the ship’s naturalist and — not letting a lack of any training or experience deter him — the ship’s surgeon as well. By January 1827, the ship had traveled to San Francisco, California, and spent the following months exploring south along the coastline, stopping regularly for land excursions, where Botta collected a variety of plants and animals for scientific study.

Years later, Botta would become famous for his archaeological discoveries in modern-day Iraq. But scientists memorialized his California collecting venture in a smaller way, with several animals named in his honor, including one of the more peculiar specimens he described as Charina bottae, or the northern rubber boa snake.

Botta was lucky to have found one, and if you’ve seen one in Wyoming, you are perhaps luckier still.

My first encounter with the snake was in June 2016 while riding my bike at the Wyoming Game and Fish Department’s Tongue River Canyon Public Access Area. It stretched out in the road, taking just a few seconds to make its way toward the safety of thick vegetation. I had seen photos of one taken by my father-in-law 30 years ago on the western slope of the Bighorns, so I knew instantly what it was and that this was a special chance to view one up close. I didn’t realize at the time just how rarely they are seen, but it was such an interesting creature that I knew I wanted to learn more about it.

My second and longer encounter with a rubber boa occurred in April, just two days after beginning research for this article. My husband spotted this one; it also was making a risky journey across the busy gravel road in the same area, and we carefully held and photographed it before releasing it away from traffic. Though my husband had sought the boa when he grew up fishing, hunting and exploring the Bighorns, he had never seen one. We each held it for several minutes, amazed at how gentle and calm it was. It made no attempt to strike or even move away from us, content to wind itself through our fingers and around our wrists. We both consider the opportunity to see this unusual animal one of our most unique wildlife experiences.

“They are a very cryptic species,” said Wendy Estes-Zumpf, herpetological coordinator for Game and Fish. “It is a real treat to actually be able to see a rubber boa. I have yet to see a live one in the wild in Wyoming. I think a lot of people may not even know we have a wild boa in the state because so few people ever get to see them.”

The northern rubber boa is one of just three boa species found in the U.S. The rosy boa, Lichanura trivirgata, is only known to inhabit California and Arizona. The southern rubber boa, Charina umbratica, is found in small parts of California, namely the San Jacinto and San Bernardino mountains.

Wyoming is at the eastern edge of the range for northern rubber boas. They can also be found throughout Idaho, Washington, Oregon, northern California and Nevada, western Montana, southern British Columbia and parts of Utah, with a few reports in western Colorado. Within Wyoming, sightings come from foothills and lower montane zones in western Wyoming, from the southern tip of the Wyoming Range, into Yellowstone and on both slopes of the Bighorn Mountains. They avoid hot, dry areas, but can be found from sea level up to 10,000 feet in elevation.

After Dayton Game Warden Dustin Shorma discovered this rubber boa in a canyon near his home, he captured the rare sighting with a photo before releasing it. Many Wyoming residents have never seen a rubber boa in the wild.


“Body rather spongy, cylindrical, attenuating a little at both extremities, one and the other obtuse,” wrote French zoologist Henri Marie Ducrotay de Blainville in the first recognized scientific description of the northern rubber boa in 1835. In other words, from a distance, you might mistake it for the largest nightcrawler you’ve ever seen.

Though they have no distinguishing patterns or markings, if you do encounter a rubber boa, it is easily identified. Unlike most snakes that have a distinct, sometimes larger head with a tapered, thin tail, the two-foot-long rubber boa is uniformly round from front to end. They are olive green to light brown with a yellow belly and smooth, soft scales.

“They are sometimes called a two-headed snake because the shape of the head and the tail are so similar,” said Estes-Zumpf.

They are a true constrictor, with rodent nestlings being a favorite food choice, but they will also take eggs, small birds, mammals and amphibians if available. Their unusual anatomic design likely serves as a ploy to would-be predators such as birds, but also as an adaptation to dealing with aggressive rodent mothers trying to protect their newborn litters when they are set upon by a rubber boa.

“They have this defensive behavior when they are being attacked where they will curl in a little ball with the head covered but the tail sticking up,” explained Estes-Zumpf. “They try to confuse predators or defensive mothers if the snake is going after a nest. They will lunge with their tail, mimicking the head. It is a unique defensive strategy.”

As a result, many rubber boa tails will show signs of scarring from bearing the brunt of attacks.

Rubber boas mate when they emerge from the den in spring and give birth to two to eight live young in the late summer or fall. Some research suggests females only give birth once every four years. However, they are a long-lived species with some individuals in the wild documented living 20 to 30 years. Researcher Richard Hoyer reported capturing a female rubber boa in Oregon in 1971 and estimating her age as at least 15. He recaptured her repeatedly over many years before taking her into captivity. She lived until 2006 and gave birth to four young in 2000, when she was well over 40 years old.
Rubber boas can live more than 30 years in the wild, although they are vulnerable to a variety of predators due to their slow pace. Their secretive nature is one of the few defenses.


These snakes are widely-recognized for their gentle, calm nature and are often used by therapists treating patients with ophiodiophobia, the extreme fear of snakes. There are no reports of rubber boas striking humans when handled. However, they are not defenseless. If handled too roughly, they can release a pungent musk that is difficult to remove.

Due to their secretive nature and preference for nighttime activity, rubber boa numbers in Wyoming are difficult to pin down.

“Their life history is such that they are a very secretive, very cryptic species,” said Estes-Zumpf. “Either they are truly rare or we just don’t see them. They will be out from dusk to dawn and underneath things like rocks, logs and leaf litter during the daytime. Their behavior makes them very difficult to find.”

Game and Fish has done no specific surveys for rubber boas, but an intensive multi-year inventory of Wyoming snakes wrapped up in 2016 with just two boas found.

“We keep track of all observations in the state, but we really have no idea what their population trends are doing,” said Estes-Zumpf. “We have no reason for concern at the moment. They are likely stable but there are potential threats that could impact populations.

“Part of the problem is we don’t have a very good idea of where to search for them, when to find them and how to find them,” she continued, noting she is planning to pursue a grant to fund a study on them. “I would like to do some radio telemetry work on rubber boas and try to get a better handle on their movement patterns and specific habitat features they use, and try to track them to den sites so we get a better idea what kind of dens they use and what we need to protect in the future.

“With all that information, hopefully we can develop a better search pattern for this species so when we go out and survey, we can detect them when they are there. Until we get a better idea how to find them, it will be really hard to assess population trends.”

Even though Estes-Zumpf believes the Wyoming rubber boa population is stable, threats to local populations due to habitat loss from road and home building or other development could be an issue. The snakes prefer cool, moist areas, particularly near streams and rivers, which is also where humans prefer to build homes and roads.

“To what extent those activities or if those activities are impacting the species, we have no idea,” she said. “Roads can fragment habitat, and they can be a source of direct mortality. They like to be out basking on roads and trails and quite a few of our records are actually of roadkill.”

Estes-Zumpf encourages anyone who observes a rubber boa in Wyoming to report the sighting to their local Game and Fish office or upload their observation on the WyoBio Citizen Science online database through the University of Wyoming at wyobio.org.  

“They are considered a state Species of Greatest Conservation Need, in part due to lack of data,” Estes-Zumpf said. “We don’t have a lot of observations because they are so hard to find. Every record of those guys is a valuable record. They are on our radar as a species we would like to learn more about.”

Christina Schmidt Shorma lives outside Dayton and recently began a new position as the public information specialist for the Game and Fish in Sheridan.


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