TDEC logo TN banner
Department of Environment and Conservation


Photo Courtesy of David Withers

By David Ian Withers

Winter in Tennessee…what images come to mind? Short days, cold nights, bright stars, barren landscapes, ice and snow…decay…and death? Sure, the bounty of fall colors is just a memory, the animals have fallen silent, all is a still, slumbering, shivering senescence. Right? Well, not exactly.

Sure, our neotropical migrants have returned to equatorial or southern hemispheric habitats, most of the frogs have burrowed into the mud for a respite, and Smokey Bear has locked his shovel in the tool shed. But to think that the party that is biodiversity in Tennessee is over is far from the truth. Look around, look down, look under. Dig deeper.

Winter may be a time when Tennessee’s myriad botanists can slow down a bit (not like they ever have to move very quickly anyway) to examine all the specimens they pressed in the preceding months. Zoologists are not necessarily so fortunate (depending on your propensity for sticking bare hands in to 30-something degree water!) A number of our more interesting native animals do their "thing" about as much in winter as they do the rest of the year, if not more so. But where are they, "if’n" we can’t see them?

Well, outside of what flies to your feeder, or steals food out of your dog’s bowl at night, they are pretty much underground or underwater…places that are not likely to freeze (too much) even in the still of winter.

While working as the zoologist with the Natural Heritage Program, I have had the pleasure of seeing some of our most interesting creatures in places where the sun don’t shine. An easy way to look at our winter occupants is topographically. There are those that are near the soil surface, under rocks or dead leaves, for instance; those that favor aquatic habitats, including surface streams, lakes, ponds, and even temporary puddles; and those that live underground, as in caves, sinkholes, or groundwater- just in winter, or in some cases, year-round.

Let’s start up on top and work our way "way down under":

Terrestrial Inhabitants

Now I don’t expect the readers of this magazine would appreciate my rambling on about every soil microbe that can be found in Tennessee dirt, nor would I pretend to want to write such a tome. Certainly, though, a number of our wingless wonders of winter do deserve mention- animals that s-l-o-w down more than they do actually hibernate (like Smokey).

Such species are known as ectotherms- animals whose body temperature depends almost wholly on that of the environment. Many of our ectotherms are familiar to you, especially if you have ever fished with live bait or kept a garden…worms, slugs, pill bugs, beetles, and the like…but other Tennessee species may be spied (or spy you) even on warm, sunny winter days.

The common Eastern Garter Snake (Thamnophis sirtalis), a resident of urban, suburban, and rural habitats, can occasionally be seen foraging about or basking in the sun.

Many ectotherms can only digest food if their core body temperature reaches a minimum temperature…compare that process to how difficult it can be to flex your hands on a very cold winter day, and you get the idea.

Since garter snakes are communal burrowers, you may find more than a few out on that unexpectedly warm winter’s day. Of course, being up, warm, and active may mean little if there is nothing to eat, so this strategy has its risks. But, if food is available, such as various invertebrates (okay, okay, "the early bird gets the worm"), then this wintertime activity can prove very helpful in keeping reserves of body fat and energy for those days that are nasty, dark, and cold.

As an aside, another Tennessee ectotherm, the Wood Frog (Rana sylvatica) has evolved to have its own built-in antifreeze…exceedingly high concentrations of glucose in the bloodstream (talk about a rush!).

As days grow short, cool, and dark, a Wood Frog’s physiology kicks in to flush its tissues with this sugar, so that the freezing point of its blood is depressed below 32 degrees Fahrenheit.

This means these amphibians can "hibernate" relatively close to the soil surface (under leaf litter) without fear of forming ice crystals in its body, which would most likely be lethal.

Being close to the surface also means that they will rapidly sense when the world above has warmed enough to get "officially" active for the new year. It is no accident that the Wood frog is, without fail, the first frog to emerge and begin breeding each new year…in some places starting in January (oh, those intrepid Capricorns!)

Not to belabor the amphibians, but the Spotted Salamander (Ambystoma maculatum) is another early riser, meaning they also stay reasonably close to the surface in winter, just in case a warm rain should come and fill up the temporary woodland pools they use for breeding.

Look for the Spotted Salamander in late winter, on rainy nights that signal them to move to breeding ponds or puddles, or look for their aftermath- large, firm egg masses in still waters in or adjacent to the forest. Sometimes their egg masses can be as large as a toy football-and almost as firm to the touch. Not surprisingly, you can find their eggs in or near the same habitats where Wood Frogs are making lots of noise!

Among the endotherms (warm-blooded) animals active in winter, the voles may be some of the most noticeable.

Often mistaken for a popular athletic program, the Tennessee Voles can be counted on to keep ground surface just a little bit more habitable than it otherwise might be.

How? Glad you asked. Voles (not moles) are rodents (genus Microtus), and as such have a propensity for making tunnels in the dead grasses and leaves which become a ubiquitous part of the Tennessee landscape in winter.

Duck and goose hunters have probably noticed their handiwork while traipsing across an old field on the way to the blind…turn back a tuft of grass and you can just about bet you will see a cross-section of a tunnel or maybe even a nest.

One benefit of tunneling as they do creates a pocket of air that may be both warmer than the ground beneath and warmer than the air above. The thermal benefits for the voles, mice, and other creatures must be remarkable, since these rodents seem so prosperous and populous!

Such a blanket of tufted grass absorbs radiant energy from the sun (and not just on sunny days!), holds the heat (think of the insulation in your house), and back-radiates it slowly into the ground-keeping all manner of winter tenants happy.

Aquatic Creatures

Fish. There, I said it. And no, I don’t have space to talk about all of them, either! Suffice to say that Tennessee has over 270 species of fish, all of which (so far as I know) don’t sleep off the winter.

Sure, they slow down, don’t eat as much, but boy, can they drink!

But rather than tackling our scaly friends (which a few other magazines target), I would like to introduce you to another ectotherm, affectionately known as bait to many fishers.

That’s right- crayfish, or crawdads- our very own decapod crustaceans- which number over 70 species in Tennessee.

I have had the thrill of working with a few ‘dads since coming here (and not in etouffee, mind you), one of which deserves special mention in our "Winter Olympics."

Nashvillians (and regular folk, too) will gladly tell you things for which our city is famous…the Cumberland River, the Hermitage, a bustling economy, that-other-university-that-isn’t-U.T., and the most recognizable of all Nashville symbols, that for which we are known the world over-the Nashville Crayfish- Orconectes shoupi.

Known only from the Mill Creek basin in Davidson and Williamson counties, this little giant put the "twang" in the Music City long before Timothy Demonbreun started trapping the area. In fact, if ever he dined on crayfish out of Mill Creek (the mouth of which is very near the cave that bears his name), you can bet he ate a few of these in a pinch.

So what makes this creature so special? For starters, Mill Creek is the only system in which it naturally occurs. It is found in the mainstem of Mill Creek, numerous large tributaries, and even some small second-order streams that eventually flow into the creek.

Because of its limited distribution and threats from continuing development of the Mill Creek watershed, the U.S. Fish & Wildlife Service listed the species as "Endangered" in 1986. The Tennessee Wildlife Resources Agency followed suit and listed the species "Endangered" under state law. O. shoupi remains the only federally listed crayfish species in the State of Tennessee, and is darn proud of it.

But what makes winter such an important time for the species? Well, to answer that question you have to know a little anatomy as well as ecology.

Starting with the latter, it is important to note the role (niche) of crayfish as the "garbage men" of the stream environment. Crayfish are often directly responsible for converting dead animals, plants and coarse woody debris (CWD) either into smaller particles ingestible by other organisms or into digested waste matter on which other organisms feed.

Beginning the decay of the tons of leaves that enter Mill Creek each fall is an important contribution of its crayfish, and Nashville crayfish are providing this service year round, without charge (try to get your leaves picked up for free!)

The Nashville crayfish, as a dedicated stream-dweller, is sleek and built for speed. It lives primarily under slab rock in areas with relatively little sediment (a precious commodity in Mill Creek!). From these watery haunts the species emerges to forage and feed primarily at night.

As a member of the genus Orconectes, the species is recognized as a non-burrowing crayfish (e.g. it doesn’t make "chimneys" or tunnels as some species do). To distinguish this species from other closely related (and similar looking) Central Basin Orconectes, one has to examine several anatomical features: O. shoupi has elongate pincers with red tips, a black band around each, and a light "saddle" on its carapace (back).

Crayfish taxonomists learned long ago that color and patterning was often not enough to distinguish species- a more intricate and intimate character was needed!

All the useful crayfish keys are therefore based on the first pleopod (gonopod) of male crayfish- a.k.a. their reproductive organ(s). Males of any of the 70-plus Tennessee crayfish species have a pair of these organs tucked underneath their hind legs. The structure of these organs, however, is unique to each species. And that makes identification possible, if not downright fun (but not so much for them).

Crayfish molt their exoskeleton at least twice per year, both into and out of a breeding molt. Typically, males molt into breeding condition in the fall (Form I), and the gonopods take on the characteristic shape which they maintain throughout the winter.

Courtship and breeding occur in fall and early winter, and females deposit eggs under their tails in late winter and carry them until they hatch in the early spring. The young actually stay attached to the female for some time, completing their first stage of growth in her protection. They then drop off and distribute themselves across the creek, stream or lake bottom. In spring, males molt out of breeding condition and into Form II, the non-breeding or juvenile form.

So, if anything, winter is probably one of the most important periods for this species, in that it is the time of year that determines, in part, the abundance of the following spring’s young.

If, in your winter romps in Tennessee creeks, you should spy a slow-moving crayfish and pick it up, don’t be surprised to find hundreds of little ones sticking close to mom through the darkest days of the year!

Dark and Loving It

Wintertime life in the the waters…and in the caves, too! Despite the scarcity of such features in West and far East Tennessee, the limestone-rich regions of the state (Highland Rim, Central Basin, Cumberland Plateau, and Ridge & Valley) are blessed with over 8,000 documented cracks, caves, and crevices.

As these features have developed over the eons, so have creatures adapted to cold, low-nutrient, dark (or nearly so) conditions moved in to exploit them.

Think of it- a place (at least on the subsurface) that seems so foreboding, so dangerous, that few other species would dare call it home- you could have the whole place to yourself.

Well, our caves are not nearly so bleak, zoologically speaking (okay, I will admit that not too many botanists can claim they go caving for work-related reasons…with one notable exception - see quiz below). Tennessee is again blessed with an abundance of species that are either cave-obligate (gotta have ‘em; a.k.a. troglobytes) or cave-facultative (love ‘em or leave ‘em; a.k.a. troglophiles).

Such taxa include our native (and cute) Eastern Woodrat, several bat species, both common and rare, at least four species of blind crayfish, one eyeless fish, beetles, spiders, flies, moths, and (depending to whom you speak) potentially four species (or sub-species) of cave-adapted salamanders.

Our true caves (having a minimum 50-feet vertical or horizontal passage) have generally one thing in common- constancy of environment- when compared to the surface, at least.

Dry caves, wet caves, upper and lower passages, tubes, fissures, cracks, sumps, domes…all the features that draw cavers underground…can all be expected to hover around 54-56 degrees Fahrenheit all year. It can be 105 outside, but a comfortable 50 degrees cooler just a few feet down. When you and I are slogging through 24-inches of "partly cloudy," cave critters are just hanging around paying us no never-mind.

Still, winter is one of the most important seasons for cave species. Bats that over-winter in caves, ostensibly hibernating, use this time to conserve stores of body fat during a time of year when their prey (flying insects) is relatively absent from the surface.

Winter is the time when pregnant bats are gestating their young- typically giving birth to only one pup per year, the following spring.

If you should come upon hibernating bats while caving in the winter, please leave them be and quietly exit the area. Hibernating bats can actually starve to death if they are roused in the winter at a time when no prey is available.

But other cave species are quite active in the winter. The Southern cavefish (Typhlichthys subterraneus), and blind cave crayfishes (Orconectes pellucidus, O. australis, O. incomptus, Cambarus hamulatus) go right on about their business as though the seasons had not changed. For them, that is probably the case. So, their activity patterns (breeding season, for instance) are determine less by clues which we accept as indicating changing seasons (like leaves falling), but more by an internal clock or in some cases, subtle changes in water chemistry.

One of our rarer rodents, the Eastern Woodrat (Neotoma magister), is active. All winter woodrats are infamous as pack rats (not unlike their European cousins found in Tennessee cities), typically occupying the transition (twilight) zone in caves - that area, which is truly neither cave nor surface, and into which at least some light penetrates.

Woodrats forage for food and nest material near the entrance of caves year-round, but put up winter stores especially in the fall (nuts galore!). They will collect bits of trash, metal, or shiny objects as well, and add that to their perched nests. It is even possible to get a rough estimate of human cave visitation by examining the amount of trash they bring in each year. That is to say, they do a pretty good job of cleaning up after ourselves!

So, whether they bask in the sun, dig tunnels for fun,

Or crawl through the night-while water's in sight,

To surpise a new friend,

With a pinch in the end

Of a fine winter's day...

Our coy comrades are still busy at a time of year when many of us "topside" figure that everybody is taking a long nap between fall and spring. Certainly that is far from the truth in the Volunteer State. This winter, forget the comfortably numb pursuits of winter's deep - the Super Bowl, the bowl games and the like and take a Tennessee hike on a wintry day.

Wintertime is just about the best season to find quiet and solitude in our countryside, and if you are lucky, and willing to look a little bit, you might just find a Tennessee creature willing to share some of that with you. Be sure to give it right back.

For more information, contact the Division of Natural Heritage at 615-532-0431.

 Quiz (for land-lubbers): Can you name a plant in Tennessee that requires botanists to imitate cavers if they want to observe it? [Hint: only one location is known in Tennessee, from Marion County.] Winners will receive a copy of the popular Tennessee Rare Plant List produced by the DNH. Send your entries to: TDEC, Division of Natural Heritage, c/o Andrea Shea, 401 Church St., 14th Floor Tower, Nashville, TN 37243-0447 or email:

(David Ian Withers is staff zoologist with the TDEC Division of Natural Heritage in Nashville.)

back to main page

Send comments to Department of Environment and Conservation.

tnhome.gif (517 bytes)tdecbar.gif (197 bytes)serinx.gif (218 bytes)sear.gif (166 bytes)gestbook.gif (200 bytes)