March 30, 2011

GARTER SNAKES – A WINTER DISAPPEARING ACT


By Margaret Gillespie, Illustration by Heather Lord

Someone had to do it! One fall day, as the leaves were changing color, I was taking my turn walking the Science Center’s coyote, ever watchful for wildlife that she might point out to me or for animals that detect her first and take evasive action. As she began investigating a sunny patch of grass and fallen leaves, a garter snake slowly curved its way forward about two feet and stopped, remaining alert with head up and tongue flickering. Coyote conveniently decided that nothing significant was there and moved on. In contrast, I appreciated this fleeting wildlife sight, for soon New Hampshire’s snakes would be disappearing from view for the winter phase of their year.

Our most common New England snake, the garter snake, Thamnophis sirtalia, has a variable pattern usually combining a narrow yellow stripe down the back with a wide stripe on each side. Between stripes is a dark checkered pattern. Garter snakes received their name because this pattern replicates the design of garters worn in the past to hold up men’s socks! Well-camouflaged, these snakes are difficult to spot and according to an article by the Canadian Wildlife Federation, “the striping makes them less visible when moving through the vegetation – the continuous line belying their movement.” Where would you look for them? Garter snakes frequent many moist places including edges of wetlands, meadows, gardens and forests as they prey upon earthworms, amphibians, slugs and insects.

All snakes are ectothermic, sometimes called “cold-blooded,” meaning that their temperature is regulated by the environment rather than by internally generating heat. That is why we see garter snakes basking on sun-bathed rocks; the warmth increases their metabolism, enabling them to be active as well as to digest food.

Now back to the topic of New England winters! How do garter snakes face the challenges of snow and freezing temperatures? They leave them behind by finding hibernacula or dens where temperatures remain above freezing, although some minor dips below freezing can be tolerated. Garter snakes generally hibernate in aggregates and have become famous in some locations, notably Manitoba, Canada where one den may hold 10,000 snakes. Their spring emergence is said to be spectacular! I suppose that depends upon how you feel about snakes in large numbers. Here in New Hampshire, smaller groups of garter snakes hibernate together in such places as old groundhog burrows or rocky outcrops, searching for a spot safe from predators and with enough moisture to keep them hydrated. As temperatures drop, metabolism in the snakes lowers, resulting in relative inactivity, although snakes respond to temperature fluctuations by moving further from or closer to the surface. According to Snakes in Question: the Smithsonian Answer Book by Carl Ernst and George Zug, reduced metabolism during snake hibernation is “fueled mainly by glycogen, a storage form of glucose, in the liver.” Liver glycogen converts to blood sugar as needed.

An essential purpose for hibernating together is close proximity to mating partners come spring. Males emerge first and are ready to compete for mates as soon as the females surface. Surrounded by males, the larger female may be in the center of a twisting, rolling “breeding ball.” Keep your eyes open for garter snakes in groups in April or May! Gestation for garter snakes is about five months so late summer and early fall can be a time to see tiny replicas of adults. Born alive, young garter snakes arrive in quantity – numbers of 20 to 40 are not at all unusual – with individuals averaging about nine inches in length.

Although the most easily seen of the 11 snake species in New Hampshire, garter snakes are worth a second look. Watch that flickering tongue (red with forked black tips) – it is part of the snake’s smelling mechanism. Wait for the snake to blink – it never will! A scale covers the eye. Hunt for where garter snakes choose to be – they have a routine which you may discover. Yes, all these observations may have to wait for spring when the snakes return – but it is always good to be reminded, during these short, cold winter days, that spring is truly just around the corner!

4 comments:

kate said...

will they move into my basement during the winter months in Massachusetts?

Squam Lakes Natural Science Center said...

Yes, it is possible for garter snakes to come into basements in Massachusetts to spend the winter if you have cracks or openings in your basement wall. They generally search for places that won’t freeze like groundhog burrows or deep crevices in rocks going into the ground but basements fit that description too. Do you think you have one? There is no reason for concern. Over the winter, garter snakes don’t eat at the cool temperatures and are relatively inactive. They will head out on their own when spring comes. It is not a good idea to move them out at this time of year because with the cold temperatures, they will not be active enough to move about and find another winter spot.

Sue H. said...

Just found one outside my kitchen door & was going to relocate it but didn't know where. We're having below freezing nights, but before I had to decide, the snake disappeared under the edge of our vinyl siding & seems to have gone up behind it. Will it survive there? I doubt it can get indoors from there.

Squam Lakes Natural Science Center said...

In an ideal situation, garter snakes spend the winter in areas where the temperature doesn’t drop below 37-39 degrees. It’s unlikely that your vinyl siding will provide that protection. The good news is the unusually warm temperatures we have been having for this time of year. Since it was active on the day you found it, likely the snake will have taken advantage of some of the subsequent warm days to find an adequate shelter for the winter.