Sunday, March 12, 2017

An Ode to the Common Gartersnake

Common Gartersnake

I love snakes, and my favorite species is the Common Gartersnake, Thamnophis sirtalis. As the name implies, this species happens to be one of the most common snakes in much of the United States. But although the Common Gartersnake is abundant and widespread, many people don't give these snakes much thought; our thoughts are preoccupied on "cooler" snake species, like Timber Rattlesnakes, or Rough Green Snakes, or Indigo Snakes. We like the flashier and the rarer species, and we oftentimes pay little attention to the common species that we see all the time. However, the Common Gartersnake is an awesome species as well, and in this post I want to shed some light on this commonly-seen, yet commonly-dismissed, snake.

Common Gartersnake Ohio

Before we jump in to ecology and the like, let's talk about names. The scientific name of this species is Thamnophis sirtalis. That's easy enough; this name was officially agreed upon by herpetologists. But then we have the common name, and you’ll find several of those. I was originally taught these snakes were "garden snakes," which is a name many people call them by. You might have heard someone call them “gardener snakes” as well. 

The real common name, however, is "Gartersnake." The people who originally gave this name to this snake did so due to its patterning, which resembled the stripes on the garters commonly worn by people back then. Since people don't really wear garters nowadays, that resemblance became lost on the general public. For many people, the name morphed into "garden snake" or the like, as this sounded similar to garter, and people would sometimes find these snakes in their garden. The altered name made sense for many people. However, in keeping with the naming tradition, the real common name continues to be the Gartersnake. There are several other species of Gartersnake in the Thamnophis genus, but T. sirtalis is the most common and widespread of those species, and is consequently called the Common Gartersnake. There are also several subspecies of the Common Gartersnake, and the one in Ohio is the Eastern Common Gartersnake, Thamnophis sirtalis sirtalis. When talking about this specific subspecies, most people drop the "Common" from the name and simply call it the Eastern Gartersnake.

Is the gartersnake dangerous

There are a couple more things to mention about the Common Gartersnake before jumping into its natural history. First, the Common Gartersnake is a completely harmless, non-venomous snake. Second, there's a myth that the Common Gartersnake will not bite people. That's not necessarily true. If you pick up a Common Gartersnake, there's a good chance it might bite you (especially if it's a female). The good news, however, is that their bite is nothing to worry about. In fact, it doesn't really hurt at all. What's the best way to avoid the bite of any snake? It's simple: keep your distance and leave the snake alone. Snakes don't like confrontation, and they won't do anything to you unless you do something to them first.

As I mentioned earlier, Common Gartersnakes are really widespread and abundant. This is primarily due to their flexible habitat preferences. Instead of requiring a specific type of habitat, these snakes can easily adapt to a variety of habitats. They inhabit forests, old fields, marshes, city parks, suburbs, and an assortment of other places. Oftentimes they prefer being near some source of water, like the individual pictured above who was only a few yards from a stream.

Just to give you an idea of where Common Gartersnakes can thrive, nearly all the individuals pictured in this post were found in this sliver of rather low-quality urban habitat. This scene is from Ohio University, near the Baker Student Center. OU's campus has several small areas like this one, with young trees and heavy groundcover. These small areas provide adequate habitat for a population of Common Gartersnakes. The specific strip pictured above contains their hibernaculum, which is a protected location in which some animals spend their winter. For ectothermic (or "cold-blooded") snakes, winter is too cold to be active; as a result, they find a protected cove somewhere within the ground (or in this case a man-made retaining wall) to overwinter in. These snake hibernacula nearly always contain several individuals (this one contains at least 15), but some hibernacula can contain hundreds, if not thousands, of individuals all spending the winter together.

As a quick aside, do you know how awesome it is for a reptile lover to have a snake hibernaculum on their campus? It's amazing.

Thamnophis sirtalis
When winter wanes, and the warmth of spring begins, the Common Gartersnakes will emerge from their hibernaculum. In Ohio, this typically takes place in late March or early April. Well, normally at least. So far, 2017 has been weird when it comes to the weather. The mild winter, coupled with many recent days being in the 60's and 70's, has made many snakes exit their hibernacula really early. In 2016, the Gartersnakes exited the Ohio University hibernaculum in mid-March. This year, the snakes emerged from the hibernaculum in mid-February, a whole month earlier. This is a pattern playing out across southern Ohio this year for a variety of organisms. Many plants are flowering or budding about 20 days earlier than they normally do, amphibians migrated about 20-30 days earlier than they typically do, and even some birds are migrating through Ohio a week or two earlier than normal. Hopefully this doesn't negatively affect the early-rising Gartersnakes, who have since been subjected to about a week with freezing temperatures, but only time will tell.

Gartersnake mating ball
When Common Gartersnakes emerge from their hibernaculum, one thing is on their mind: it's time to mate. Males will emerge first, waiting around the hibernaculum exit for the females. Once the females emerge, the males will begin vying for the chance to mate with a given female. You end up with scenes like the one above, often described as a "mating ball." In this instance, two males are both trying to mate with the single larger female. Interestingly, both males might end up being successful. A female has several eggs available, and each egg can end up being fertilized by a different male. This results in mixed paternity, where a single clutch of a female's offspring might be the result of several males. This is really common in Gartersnakes, with up to 70% of all clutches exhibiting mixed paternity.

Even more interesting is the fact that the Common Gartersnake gives live birth. Most, but not all, snakes lay eggs, which then hatch out on their own. The female Common Gartersnake, on the other hand, never lays her eggs. The eggs get fertilized by the males, but then stay within the female. These eggs then develop and eventually hatch within the female, who then gives birth to juvenile snakes instead of the eggs like most other snake species. Although this appears similar to how mammals give birth, it is quite different. With mammals, the female actively exchanges oxygen, food, and other substances with the growing fetus. With live-young-bearing snakes, however, the female never exchanges anything with the fetuses. Instead, the eggs in which the fetuses are contained in have all the substances required for development; the female simply carries these eggs inside of her instead of depositing somewhere in a nest or the like.

Thamnophis sirtalis Ohio

Like other reptiles, Common Gartersnakes are ectothermic (AKA "cold-blooded," but that isn't really a good term as their blood isn't always "cold," and it can actually be warmer than the temperature of our blood). Ectothermy is where an organism doesn't produce its own body heat through metabolic processes, but instead relies on environmental heat. We humans are, on the other hand, endothermic, meaning we create our own body heat through metabolic processes. When an organism is ectothermic, they are at the mercy of the environment. If it's too cold outside, an ectothermic animal cannot function and may die. If it's too hot, that ectothermic animal also can't function and may die. As a result, ectothermic animals must thermoregulate, meaning they must regulate their body temperature by either moving to a warmer location or moving to a cooler location, depending on their current need. Common Gartersnakes do this by basking in the sun when they want to heat up, or retreating to a shaded area when they want to cool down.

Melanistic Common Gartersnake
Because of the thermal constraints placed on Common Gartersnakes, one could imagine that any sort of characteristic which makes them stay warmer would be advantageous. A common example of this melanism. Melanism is a condition in which an animal has an abnormally high level of melanin in their skin. Melanin is a dark pigment within the skin of most organisms that gives rise to dark coloration. The dark stripes running down the body of most Common Gartersnakes are a result of melanin. Sometimes there will be a mutation in the melanin-regulating genes of a Gartersnake's DNA, and those genes will create way more melanin than they should. The result? A completely black Common Gartersnake, just like the one pictured above.

Melanistic Thamnophis sirtalis

Melanism is a normally occurring, albeit rare, condition (like albinism) within most animals, but we don't see many melanistic animals because being melanistic normally isn't an advantage. However, being melanistic is a big plus for Common Gartersnakes. The color black absorbs all the wavelengths of the white light of the Sun, so a melanistic individual can absorb more heat energy than a normal-colored individual. In fact, one study found that melanistic individuals were able to stay about 2°F warmer than their normal counterparts. In the northern portions of the Gartersnake's range, where the temperatures are much cooler, this ability to remain relatively warmer gives melanistic individuals an advantage; they can be active earlier and for longer periods of time, meaning they can hunt more and end up growing bigger. These melanistic individuals end up doing better than the normal individuals, and the melanism-causing genes end up being passed on to more and more baby snakes. This selective advantage has resulted in up to 50% of the Common Gartersnakes around the Western Basin of Lake Erie being melanistic. The individual pictured in the last two photos, for example, was from this region.

Thamnophis sirtalis Ohio
Speaking of feeding, what do Common Gartersnakes eat? It turns out they feed on a variety of organisms. Common Gartersnakes primarily feed on worms, insects, small crustaceans like crayfish, and amphibians. Larger individuals will occasionally hunt down baby birds, lizards, other snakes, and small mammals such as mice. However, Common Gartersnakes must also watch their back, as they are sometimes eaten by larger animals such as other snakes, birds, and small to mid-sized mammals (such as raccoons and even shrews!).

Eastern Gartersnake Ohio
The Common Gartersnake is probably the most abundant snake species we have in Ohio. This species lives in every single county here, and you can probably find one if you keep a sharp eye out while hiking through appropriate habitat. They're beautiful snakes in my opinion, and I can't help but get excited every time I see one. Next time you see a Common Gartersnake, take a closer look!

Thanks for reading!

1 comment:

  1. I can assure you that the bite of a garter snake can be quite painful. I was once bitten by a captive garter on the fleshy area between the bases of the thumb and forefinger..... and the snake would not let go. I had to carefully pry the reptile's mouth open with a plastic pen to escape its' vice-like grip. I hurt plenty.