An "Aberrant Eastern Gartersnake"

Plains gartersnakes (Thamnophis radix) are a common species from south central Canada through the Great Plains to Texas and Oklahoma.  Across this expansive range, their populations can reach densities of 300 individuals per acre.  They are not a rare snake by any stretch of the imagination.  In Ohio, however, the entire range of this species is restricted to just one county within one prairie remnant (and not even the entirety of that).  Ohio plains garters are snakes out of time.

5,000 years ago, the climate in Ohio was very different than it is today.  The Xerothermic period, as it is called, was significantly dryer and hotter by as much as five degrees Celsius with 25% less rainfall.  For several thousand years, Ohio’s climate closely resembled modern day Kansas.  This warm, dry period was marked by an expansion of western biota into the state.  Flora and fauna that we associate with the great plains, found suitable habitat in this “prairie peninsula.”  When the climate shifted again (to the cooler, wetter present), the prairies receded, leaving behind a few isolated prairie pockets where clay soils inundate the landscape for much of the year (such as on ancient riverbeds), preventing the expansion of forests.  Today, agriculture has reduced the 12,000 ha of contiguous wet prairie across northwestern Ohio to a few thousands disjunct hectares.  

The entire Ohio Plains Garter population is so localized that these snakes were not verified in Ohio until 1945.  Even the great herpetologist, Roger Conant, who collected the first specimen in 1931, mistook the washed-out DOR (dead on road) snake for an “aberrant eastern gartersnake.”  This is the ultimate case study in local abundance.  While these snakes would have originally inhabited a larger expanse of the available prairies in Ohio, habitat loss and land-use changes have reduced their already limited populations by as much as 94% in some areas.  Where they still occur, there can be hundreds per acre.  However, the sympatric eastern gartersnake (Thamnophis sirtalis sirtalis) outnumbers the plains by about ten to one.  If I had any hopes of finding a plains, each and every striped snake I discovered would have to be thoroughly examined.

A terrestrial crayfish burrow 

In preparation for a long week of finals, my girlfriend, Julia Joos, and I decided to take a weekend herping trip to unwind.  We arrived in northwestern Ohio in the evening, anticipating an early morning search the following day.  The weather, however, had other ideas.  That night brought storm clouds and frigid temperatures that stuck around until late afternoon.  The clouds finally burned off just a few hours before sunset.  We hoped the timid sunshine and mild temperatures would be enough to entice the snakes to bask. 

The flat expanse of fields and croplands intermitently bisected by roads might not look like much to the passing observer, but I could tell right away that this habitat was great.  Hollow mud chimneys—the entrances to the burrows of the terrestrial crayfish species Falicambarus fodiens—were everywhere.  These burrows are not only a sign of high water quality and good soil chemistry, they also provide the snakes with refugia during inactive times of the day and year.  Modify the water table or introduce pollutants that wipe out the crayfish, and the snakes will invariably disappear along with them.  

In early spring, the vegetation is still brown and brittle, weighted down from months of snowpack.  With their lateral stripes, gartersnakes camouflage perfectly among the criss-crossing network of dried reeds.  I hiked quickly, scanning the ground and listening for rustling movement.  Julia was more careful.  She found the first snake of the day in a spot I had tromped right over.  It was an eastern gartersnake, still muddy from the crayfish burrow it had recently emerged from.  During the next hour, we found half a dozen more garters, but none were quite what we were looking for.  I finally resolved to photograph one of the more colorful individuals coiled up among the mud and grass.  As I set up my camera, Julia called out from just over my shoulder.

“Oh, here’s another one!” she said.  I turned around to see a large gartersnake coiled among the grass.  “Nope!” I laughed, “that’s our radix!”  Had I not been looking for the subtle defining characteristics of the plains garter, I easily could have passed this snake by.  Even through the snake’s mud-dusted scales, I could tell its stripes were unusually black.  The dead giveaway that this was our plains garter, however, was the yellow-orange stripe running the length of the garter’s back.  Out of the hundreds of variations of the eastern gartersnake that I have seen over the years, none have had a stripe quite that color.

The garter cooperated nicely, coiling in front of us and tongue flicking.  After a few shots the snake decided it had had enough, and zipped away through the grass.  The purpose of those stripes becomes clear when a garter flees through a vegetated landscape.  longitudinal stripes make it significantly harder to judge the snake's speed, length, and direction.  The plains garter seemed to almost meld with the landscape it so depends on. 

A juvenile plains gartersnake (Thamnophis radix)

On a return visit to the area a few weeks later, I was lucky enough to find a juvenile plains gartersnake, a good sign that these endangered snakes are breeding.  Despite the perilous predicament these snakes find themselves in, very little management is directed towards their conservation.  Reintroduction efforts through captive breeding have been underway for years, but these snakes still face a host of threats in their final stronghold.  The landscape they call home is primarily managed for waterfowl hunting.  Scheduled mowing of their field habitat has been shifted to coincide with snake inactivity, but individuals are still occasionally killed.

Like that first specimen found by Conant in the 30s, road mortality is one of the easiest ways to discover this species.  I found a large adult T. radix, carelessly crushed by a speeding vehicle as the harmless snake attempted to cross between habitat patches.  Even though plains gartersnakes are common across the great plains, the disjunct populations in Ohio, Missouri, and Illinois all represent unique genetic lineages.  They are important contributions to the biodiversity of our state and to the persistence of these remaining prairie patches.