Stalking bullsnakes on St. Croix Valley sand plains

In a prairie on the river bluffs, researchers are slowly and steadily learning about the region’s largest snakes.




10 minute read

A bullsnake that is only a week or two old. Its eye is blue because it has not yet molted for its first time. (Greg Seitz, St. Croix 360)

On a dry prairie above the St. Croix River in eastern Minnesota, little snakes become big snakes. 

The prairie stretches for hundreds of acres. It is sun-baked and windy, the soil is mostly sand, left here by melting glaciers. Scrubby grasses grow in clusters separated by patches of coarse bare ground. These conditions are comfortable for bullsnakes. A subspecies of gopher snakes, bullsnakes (Pituophis catenifer sayi) are the biggest snakes found in St. Croix River country, reaching up to six feet in length.

But they start life a little over a foot long, hatching in burrows, hanging out with their siblings in sunny openings, and trying to survive. While the species nests and hibernates in rocky cavities in other areas, not much was known about how they used sandy places like this until recently.

Bullsnakes are designated as a species of special concern in the state, facing numerous threats. New knowledge can help conservation.

Studying snake survival

Researchers, land managers, and volunteers with the Minnesota Department of Natural Resources have been studying this particular population of bullsnakes for the last decade, and are starting to understand what they need to survive.

I joined a team consisting of Carol Hall, a DNR herpetologist with the Minnesota Biological Survey, and snake enthusiasts Kris Backlund and Dave Crawford, on a sunny day in early September. The young snakes hatch around this time, and we hoped to find both babies and adults.

(Note: Wildlife poaching is not only a problem on other continents, but in the Midwest, too. Illegally capturing reptiles for the pet trade is a significant threat to bullsnakes and other species in Minnesota and across North America. For that reason, St. Croix 360 will not disclose the location of these snakes.)

Our group set off across the large restored prairie at mid-morning, golden grasses stretching to the distance. Despite looking a little like an overgrown desert, the dry prairie was a lively place, full of insects, unseen birds cheeping, unique plants, and plenty of signs of snakes. Before we found any live ones, the seasoned searchers spotted several shed skins from snakes that had molted.

My guides told me the snakes prefer this prairie because the soil is sandy and soft enough for snakes and their prey to burrow into. It is comprised of sediment carried by glacial meltwater, and is just right for snakes to survive long, cold winters, summer fires, fungal diseases, and anything else the world throws at them.

“The snakes prefer nesting sites with just the right amount of heat and soil moisture,” said Crawford.

Rodent exterminators

Kris Backlund of the DNR holds an adult bullsnake. (Greg Seitz, St. Croix 360)

Many people are afraid of snakes. While there are species that are poisonous and dangerous, and I suspect the fear is quite natural and exacerbated by culture, snakes are essential to our ecosystem. 

For one thing, bullsnakes are rodent exterminators. Spending much of their time in small mammal burrows, the snakes are specifically suited to hunt the creatures which can cause problems when overpopulated. 

Crawford says just one bullsnake can save farmers an average of $400 a year by eating the mice, gophers, and other animals that would otherwise damage crops. Eating rodents also helps reduce the number of deer ticks and the serious risks of disease those parasites carry.

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Even as six-foot constrictors, bullsnakes are not dangerous to humans. They will bite if cornered, but their fangs carry no venom. A potentially painful bite is a risk the researchers acknowledge – and they routinely carry band-aids. Bullsnakes do have a habit of coiling up, hissing, and rattling their tails when afraid, too, which can seem enough like a rattlesnake to scare most people.

Like all wildlife, people should observe snakes in natural state but are not advised to attempt handling them.

But bullsnakes mostly want to be left alone to mate, hibernate, and eat rodents. The thing is, they can’t survive the winter in a cornfield, and they can’t reproduce in a forest. For that, they need places like this prairie.

Prowling the prairie

An adult bullsnake passes through prairie near the St. Croix River. (Greg Seitz, St. Croix 360)

We prowled the prairie, spaced 10 to 50 feet apart, heads down, eyes roaming the ground. 

For the first time, I noticed all the little holes in the soil, never having paid much attention to the relative abundance of rodent burrows underfoot before. It seemed like one burrow per every few square feet.

Gophers and mice can be a nuisance to humans, and snakes help keep their numbers down, but the rodents are also important to the health of grasslands. They keep the soil loose and aerated, and their mounds of fresh soil at burrow entrances let new plants germinate. 

The rodents help support diverse plant species and the birds, pollinators, and other creatures that depend on them. The bullsnakes help ensure a careful balance is maintained.

I was lost in a reverie of pebbly prairie soil and stiff stalks of multi-colored grasses when Backlund called out that she had found some hatchlings. She stood with lively handful of yellow and black baby snakes, holding them carefully to avoid harming them.. 

The rest of us walked over for a closer look. Carol knelt, removed her backpack, and proceeded to initiate these young snakes in the research project. 

Working with her partners, she measured, weighed, and photographed each specimen, writing down all the details. It was kind of like filling out their birth certificate. Some of the snakes got tags the size of a grain of rice so they could be identified in the future.

Feisty fun

Kris Backlund holds a bullsnake hatchling. (Greg Seitz, St. Croix 360)

This is when their unique personalities shine. Even week-old hatchlings respond different to their human handlers. 

In Kris’s words, some snakes start out “feisty,” while others are more docile. The survival rate for vulnerable, inexperienced young bullsnakes is low, meaning only a small percentage of the hatchlings will survive four years to breeding age. The researchers wonder if “feistiness” translates into success finding food or winning a mate, so the more aggressive snakes might have a better chance of living to adulthood. 

That’s another question that can be considered thanks to the data the team collects.

Then the snakes were let loose, and they slid away, disappearing faster than I could believe among the sparse grasses and bare soil. They are covered in patterns and colors that conceal them almost anywhere.

“Their patterns really work as camouflage in many different habitats,” Hall said.

The first find was quickly followed by others. We were approaching a known nesting area, where there are usually lots of young found on an imperceptible slope near woody cover.

Bonding with bullsnakes

DNR biologist Carol Hall weighs a bullsnake hatchling. (Greg Seitz, St. Croix 360)

Out here in this well-studied prairie, each burrow has a nickname. Many of the clumps of grass or weathered old sticks are also familiar reference points.

Kris, Carol, and Dave had done this many times. When one of them spotted a few hatchlings hanging out in the opening of a burrow, they moved forward quickly with one hand outstretched. The snakes can retreat back underground when threatened, so surprise is essential. 

More often than not, the researchers would stand up with a handful of baby bullsnakes. They paused to admire, assess, and document the reptiles, then resumed their search.

In 2013, Crawford published an article about the early days of the study in the DNR’s Minnesota Conservation Volunteer magazine. He has spent countless hours and walked hundreds of miles following snakes around these lands, getting to know their behavior and their burrows.

“The most fascinating behavior I docu­mented on video in 2012 was male versus­ male combat over females during the April-May mating season. Just as two white-tailed deer bucks get into shoving contests, male bullsnakes compete for mating privileges. If you’re a species with no arms or legs, how do you set up a contest with another male? You head-wrestle. Two males come togeth­er and travel parallel to each other, each try­ing to press the other’s head to the ground with its own head.”

Serpentine Science, Conservation Volunteer, July-August 2013

For a couple years, the team attached radio transmitters to snakes, which allowed them to follow the animals all season using telemetry. It was painstaking work which divulged interesting aspects of bullsnakes’ lives.

The tracking effort let them follow one of the female snakes when she swam across the St. Croix River, spent time in Wisconsin, and returned to this prairie to lay her eggs. The researchers say they’ve observed snakes travel a mile or more from the prairie, into surrounding private lands, to feed, likely mate, and simply spread out during the summer.

Ranging and roving

Dave Crawford with some new discoveries. (Greg Seitz, St. Croix 360)

“They can spend half their above-ground season” outside the protected prairie, Crawford says. While ensuring the nesting and wintering area remains suitable habitat is important, so are the actions of private landowners whose property hosts snakes for part of the year.

Crawford explains that this particular type of prairie “mosaic” is great for snakes because it includes lots of openings where the sun can reach the ground. Many fields of nonnative grasses form a dense carpet which may be good for mice, but is too cool for their reptilian predators.

Because snakes are cold-blooded, they depend on the air and the soil to keep them warm enough to hunt and breed. On a sunny day such as this, the young ones soak up the sun in their burrow openings, hoping to gather the energy to try to find something to eat. 

They only have a short time before their first winter.

The snakes survive the frozen season by using gopher burrows that go below the frost line for hibernation. Crawford says the older snakes often go into hibernation earlier than smaller snakes, probably because they have more bulk to last them through the winter. 

Older snakes can claim the best burrows, and the young are left to prove their mettle, bulk up, and then find somewhere to hide from the coming deep freeze.

A big one

I had to leave that afternoon before we found any adult snakes. While the hatchlings hang out near their nests, the adults range across the landscape, tongues flicking to smell their surroundings, deaf to sound but sensitive to the slightest vibrations. They are more spread out, and not so easy to sneak up on.

Two weeks later, Backlund texted me to say she found an adult bullsnake, so I met up with her again on a sunny Monday morning. 

This snake seemed unsettled, perhaps one of those snakes that started out feisty. Once removed from its temporary quarters in a plastic tote, it struggled to escape or strike Backlund, or both, while she went through all the steps she must before releasing it back into the wild. Measuring a snake which is trying to curl around and bite the measurer is a particular challenge.

After scanning it for a tag (similar to a microchip in pets) several times, Backlund determines it doesn’t have one, which means it will get one.

She sits on the ground, holds the snake with her feet and hands, and inserts a needle between some scales, injecting the tag that will let them identify it in the future. She also probes it to determine the sex, basing a determination that it’s female on the size of a hidden opening near the base of its tail.

Then the snake goes back in the box and back in the car and we drive a short ways to the prairie to release her.

Sensitive species

Bullsnakes and the ecological balance they represent are at risk in their home territory. The threats are numerous, from the poaching mentioned earlier to the loss of the specific habitat types they depend on.

As row crop agriculture and development expands, not only are the snakes’ homes destroyed, what’s left is increasingly isolated. When the snakes can’t get to other habitat, their population is restricted, and genetic diversity declines. 

Up until just two years ago, it was still legal to collect bullsnakes for the pet trade or other purposes on private lands in Minnesota. All reptiles are now legally protected from collecting in the state.

Many bullsnake populations are also essentially “islands” surrounded by unsuitable habitat. Traveling any distance is dangerous because of road crossings. So the loss of one particular piece of habitat for food, mating, or hibernating can end a sizable portion of the population.

“Today, bullsnakes are primarily restricted to protected areas of the state that have not been developed or converted to agriculture,” said Christopher Smith, a St. Croix Valley wildlife biologist who is not involved in the research project but has studied reptiles extensively. “Habitat loss is the biggest threat to bullsnakes in the St. Croix Valley. The majority of remaining populations now occur on large tracts of protected land.”

Some of the adult snakes Backlund sees are on the roads surrounding the prairie. Sometimes they are alive, sometimes not. The researchers urge drivers to watch for snakes and avoid them.

Finding freedom

At the edge of the prairie, Backlund sets the tote down, takes the lid off, and tips it on its side so the snake can slither out. Despite the snake’s feelings about being confined, she is slow to leave, cautiously flicking her tongue to smell the breeze.

Slowly she slides out of the box and through the grasses. She is not in any hurry, but it’s hard to guess what a snake is planning.

Backlund and I follow her for a few moments, watching as the snake’s long body weaves around the grasses. Backlund has to leave, but I stay there, still trying to get photographs of this unique creature in its unique natural habitat.

It’s breezy out here again and the sun is shining, but October is next week, and soon the warmth will be gone. A snake like this will soon be underground until next spring.

Her unhurried pace and wandering path belie a purpose that is soon revealed. I start to lose sight of her behind some grasses, and before I know it all that’s left is her tail sticking out of a burrow, and then that too is gone. 

She wasn’t wandering, she was circling this hole in the ground, seeking out refuge, or maybe a meal. The snake study has shown that they will reveal their ways to anyone willing to watch long enough.

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9 responses to “Stalking bullsnakes on St. Croix Valley sand plains”

  1. Mark Hove Avatar
    Mark Hove

    Neat article! Thanks Greg.

  2. Christopher E. Smith Avatar
    Christopher E. Smith

    Great article. Thank you.

  3. Russ Hanson Avatar

    We see them often in Sterling Township, Polk County, WI. A photo from this summer of one swallowing a big frog or toad.

    1. St. Croix 360 Avatar
      St. Croix 360

      Very cool! Amazing photos.

    2. carol Avatar

      Hey Russ, Thanks for sharing your photos! The species you found in Polk County, WI was an Eastern Hog-nosed Snake (not a Bullsnake). The two species occupy similar habitats but Bullsnakes prefer small mammals and birds, vs. the Hog-nosed snake’s preference for toads (as you nicely captured!). Carol

      1. Greg Seitz Avatar
        Greg Seitz

        Thanks for the chiming in with the expert info, Carol!

  4. Patrick Collins Avatar
    Patrick Collins

    Great article Greg!

  5. Lee Kisling, Hudson, WI Avatar
    Lee Kisling, Hudson, WI

    Wonderful thorough article! I have a really good short film of a Western fox snake – if the writers would like to see it, let me know:

  6. Diane Avatar

    Thank you for describing this snake’s habitat, it explains why I’ve never seen snakes in the vicinity of our small stormwater lake where the soil is heavy with clay and perhaps temperatures are too cool and wet.


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Stalking bullsnakes on St. Croix Valley sand plains