Snakes on a Plain

Our month of change is coming to a close. May is an amazing month out here. In the space of only a few days, we witness a stunning transformation. In the blink of an eye, we manage to go from a barren landscape, just recovering from the ravages of a northern winter to a lush and verdant pastoral scene. Everything wakes up in May. Buds that have been straining against their confines finally burst free, the air fills with the scent of fresh pollen and the busy sounds of returning birds. Insects emerge from their hiding places, crawling out into the newly warm sunshine, but they aren’t the only creatures to find their way out of the darkness.

Up in my neck of the woods, we get to witness something truly remarkable. Every May in central Manitoba is marked by the emergence of the largest concentration of snakes in the world.

In a nondescript piece of prairie and aspen parkland, over 50,000 red-sided garter snakes (Thamnophis sirtalis parietalis) emerge after a six month sleep from large caves in the limestone bedrock, bringing the underbrush to life with their constant slithering.

So what makes this nearly 12,000 hectare bit of scrubland snake mecca? As they say in real estate: location, location, location. It’s not the habitat above the ground that counts, but what’s below it. Much of central Manitoba is underlain by layers of limestone and dolomite, dating back 300 to 500 million years ago.  Limestone can be dissolved by water and over time, it has eroded away large hollows in the area, creating a formation known as karst topography.  You can find crevasses and caverns of different shapes and sizes all over the Interlake region. I have quite a few further north in the forests I call home, but none are quite as large as the network of five caverns that crisscross under the Narcisse Wildlife Management Area.

They’re also pretty deep, stretching down below the frost line, which is what makes them so attractive to snakes, because unlike many other cold-blooded critters, snakes don’t keep well in a freezer. So, after waiting out the worst of the cold, their internal clock tells them it’s time to wake up, sending the snakes up to the surface.

When that happens at the Narcisse dens, it’s a sight to behold: thousands of snakes, milling about in the dens and and

Red-sided garter snakes at the dens in Narcisse, Manitoba

surrounding areas. They stick around for almost a month after they first glimpse the sunshine because this is one of the few opportunities for this otherwise solitary creature to mix up the genetic pool. As soon as they emerge from the dens, females are literally pounced upon by dozens of males, forming something biologists delicately describe as a ‘mating ball’. Males jockey for position, trying to be the one to get his sperm to the eggs. Because females can store the sperm before fertilization, it’s likely her young end up being the product of more than one father.

By the end of May, however, the furor dies down. Knocked up and ready to go, both males and females disperse to spend the summer feeding and, in the case of the females, giving birth. The dens and other hibernacula sit empty for the summer, but as the song says, we’ll see them in September.

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Coming out of the Woodwork

Spring is sort of a fickle thing around here. I was so sure we’d seen the last of the snow, then I woke up to white and howling north winds over the weekend. The only saving grace was that it didn’t last for long.

Weather isn’t a very reliable indicator of the seasons up in the north woods. I’m pretty sure the only month I haven’t seen flurries of some kind is July. However, there are plenty of other indicators of the impeding spring.

While returning birds are always a good sign, it’s when I see my first butterfly that I know we’re finally starting to thaw for the year. Usually sometime around early April, I spot one, a Mourning Cloak (Nymphalus antiopa, pictured) or an Eastern Comma (Polygonia comma), basking on a branch or the middle of a gravel road, soaking up the now warmth-giving rays.  It’s always an especially fun juxtaposition when I find one sitting on top of some snow that just refuses to melt and it makes me wonder: what is a cold-blooded insect doing up and about so soon in the spring?

The reason these butterflies can get an early start on things is because they spend the winter hibernating as adults. Actually, calling it hibernation is putting it lightly. They tuck their delicate bodies into old woodpecker holes, cracks in the tree bark or between the shingles and wall boards of old or unheated buildings and then they simply let themselves freeze. Okay, well not quite. While they do let ice invade their bodies, these butterflies are quite particular about where the crystals form, keeping them confined to the fluid on the outside of their cells so that vital systems aren’t destroyed.

As the days get longer and warmer, they literally come out of the woodwork, flitting around in the sunshine, even when there is a foot of snow on the ground. How these butterflies and other freeze-tolerant organisms know when to wake up is still a mystery. They’re basically in a state of stasis all winter, their lives set on pause, so what exactly constitutes their alarm clock is still an unknown.

Once they’re up and at it, however, there is no time to waste. Mating begins right away, with males and females fluttering around each other before settling down to business. Once the eggs are laid on suitable host plants, like willow, aspen and birch, these harbingers of spring die off, leaving their genetic legacies to the next generation. It may seem like a short life, but most of these over wintering butterflies have been alive as adults for up to 10 months, veritable ancients for their world.