In early March, a friend was out walking the river trail at the Nisqually Wildlife Refuge. It was an unusually warm sunny early afternoon when he stopped to admire some frogs in a pond. While watching the frogs, suddenly at his feet he noticed a seething mass of garter snakes. He told me he saw several large ones, and then a large wriggling ball of snakes (a mass of male snakes trying to mate with a female). He had stumbled upon a winter snake den or hibernaculum.
This is what garter snakes do in winter. They find a convenient depression in the ground, below the frost line, but above the water table and there with hundreds of their compatriots they hole up for the winter. As cold-blooded animals they do not enter a true hibernation state, but use the protected space and the shared heat of the other inhabitants to get through the winter months. In our area, in early March, on sunny days, you can often find these snakes making their first spring forays out into the world. This is what my friend had found.
I've long had an interest in garter snakes. I grew up with six siblings on the rural edges of Olympia near Hazard lake, and we had miles of abandoned cow pasture to explore. I remember with great fondness how I would catch a garter snake, and then menace my younger siblings with it. Even now, the memory of the terrified screams of the young'uns, running for their lives, warms the cockles of my heart. (Yes, I was a BAD sister.)
My friend JoAnna and I decided to go out to the refuge and see if we could find this hibernaculum. Armed with detailed directions, we walked along the river trail and found a certain middle-aged Black Cottonwood tree, growing out of the raised dike that keeps the Nisqually river at bay. This tree has a fat root that is only partly embedded in the soil; underneath it is a perfect dry location for snakes. And about noon each day, the sun comes out and shines with full strength on this site. That is enough to bring out the snakes.
In our first visit we sat and watched for awhile and saw nothing. We were about to leave when another refuge visitor passing by looked down and remarked: "Look! Snakes!" Apparently it had warmed up enough and the snakes were starting to come out to bask. We got up in a flurry of excitement and watched for a couple hours. We estimate we saw about 30 snakes on that visit.
We've visited the snake den a few times now. Each time we learn more about the garter snakes and their habits. In our most recent visit Glen came along, which was great, because we managed to persuade him to pick one up. Glen is a skilled snake wrangler, and made it possible to get some great pictures. He also held the snake long enough that it got unhappy; it produced a pea-size drop of pink poo from its cloaca and the stench was palpable several feet away. I didn't get a picture of that.
I sent a few pictures along to Bill Leonard, a local herpetologist who very kindly answered my emails. It turns out we have 3 species of Garter snakes in western Washington. It turns out all three species can have a wide range of colors, but if you look at head size, and count the scales above and below the lip, you can sort out the different species. Bill is a co-editor in the book Reptiles of Washington and Oregon, which helps you learn how to do this.
The snake that Glen held is probably a Western Terrestrial Garter Snake, based on labial scale count. These snakes are widespread and commonly found near water. They feed on slugs, snails, earthworms, fish, salamanders, frogs, lizards snakes and even birds. Females are typically larger than males. These snakes may live as long as 10 years.
The snakes we saw at the hibernaculum were probably males. The story goes that on sunny days in early spring, the males emerge first, to bask and to keep alert to the scent of a likely female. If one appears, every male snake in the vicinity will try to mate with her, which is how my friend saw a snake ball. Once mated, the females leave the den and head for likely foraging territory. The males may stick around for awhile, and then they, too, will disperse. Come early October, many snakes will return again to the same hibernaculum, using it to help with their winter survival. We plan to keep our eyes on this hibernaculum for some weeks to come.
You can help garter snakes prosper in your own backyard. At the end of this blog entry, I am posting a link to a description of how to build a backyard rock pile (Glen and I are in the process of putting one in as we speak). A more simple addition is a snake board; this is described in the Washington Fish and Wildlife webpage. We hope you enjoy these fascinating animals!
• Fish & Wildlife info about snake boards: http://wdfw.wa.gov/wlm/living/snakes.htm
• Info about Rock Piles: http://www.wildlifegardeners.org/forum/habitat/1413-log-piles-rock-piles.html
• Check out Manitoba's Narcisse Garter Snake Dens: www.manitobaphotos.com/narcisse.htm
• Thanks to Bill Leonard for answering my questions.