The world’s largest aggregation of snakes

July 28, 2015 • 9:15 am

Since Greg is posting twice about snakes this week, I declare it Official Website Snake Week.™

My colleague Steve Arnold used to work at my university, and since his research was partly on garter snakes, I knew about the amazing mating aggregations of that species that occur in some locations. But by far the largest aggregation is in Winnipeg, Manitoba, as reported in National Geographic and called to my attention by reader Taskin, who lives near the snake mosh pit:

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The pit contains 75,000 garter snakes writhing about in a space the size in your living room! To see the 3.5-minute video, click on the screenshot below (TRIGGER WARNING: LOTS OF SNAKES!), which also takes you to the article.

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Christine dell’Amore’s piece gives all the information you want to know, and if you’re a woman, you’ll feel a special pang. A few snippets:

Each spring, masses of red-sided garter snakes congregate inside limestone caves to form mating balls, in which up to a hundred male snakes vie for a single female. She, in turn, “is desperately trying to get out of the pit,” said Colangelo, an environmental documentary photographer.

These slithery swarms appear to be a “frenzy, but a closer look reveals a much finer dance,” Colangelo said in his field notes. “The small males court the larger female by rubbing her head with their chins and maintaining as much contact between their long bodies as possible.”

. . . Why is this the largest gathering of snakes? What attracts them?

This grouping of red-sided garter snakes has the most northern range of any reptile in the Western Hemisphere. It’s due to a lucky coincidence of two geological features: limestone crevices and marshes. It’s a fantastic place for snakes to be in the summer because there are huge marshes loaded with frogs, but in the winter it drops down to -40. The only reason all these snakes can survive these winters is because of the large limestone crevices that reach deep into the ground, below the frostline. They spend about eight months of the year in these large underground chambers. They come out in the spring, mate in these dens and [then travel] up to 20 kilometers [12 miles] to their summer grounds, load up with amphibians and worms, and head back to the cave. (See National Geographic’s pictures of snakes.)

. . . What’s interested you the most about the snake pits?

Mating balls are the most intriguing part. All of the males come out first and hang out at the base of the pit, and females are instantly mobbed. The females then give birth out in the summer grounds, in the marshes. The curious thing is that those newborns are immediately abandoned. None of those newborns return to the dens. They find spots in the summer grounds to overwinter. Not much is known about why they don’t migrate to the dens or how they survive the winter. (See more of National Geographic’s snake videos.)

Yep, it’s a tough life for female garter snakes. . . . and female ducks, dragonflies, H. sapiens, and a gazillion other species. Evolution is a cruel process, and this demonstrates that if it’s the product of God, God doesn’t like females. But we already knew that. . .



23 thoughts on “The world’s largest aggregation of snakes

  1. To make it worse, I’ve heard that it’s not at all unusual for a female to be suffocated by these writhing clumps of horny males!

  2. Fascinating as they are, Indiana Jones and I are in complete agreement on snakes! Just can’t help it!

  3. Wow! This is great. One of my earliest memories (I was probably about four) is of a ball of garter snakes in a roadside ditch near the house I lived in in Minnesota during early childhood. I remember wandering down the driveway toward the road on one of those grand childhood journeys (all of about 100 feet, probably). The sight of the writhing ball of creatures was fascinating and I recall watching it for some time with wonder. Then I recall enthusiastically running back up to the house to tell my mother about it only to get seriously dressed down for wandering so close to the road without permission – not to mention getting so near “those nasty snakes”. Never saw anything like it since and always thought it might have been one of those childhood fantasies. Nice to get some corroboration that I wasn’t just imagining it. Thanks!
    (By the way, my mother was a very nice woman in many respects and I loved her. She just had a bit of an over protective streak.)

  4. A question: I assume that the assertion that the newborns don’t return to the den should be interpreted that they don’t return their first year. I assume that they eventually must make their way to the dens. Anyone know?

    1. Not sure about garter snakes, but the Prairie rattlesnakes that we studied in Alberta gave birth relatively near the winter dens. The females would stay with their broods for a few days after parturition, and then move off towards the dens, leaving scent trails that the neonates could follow. Quite possibly these garter snakes do the same sort of thing – like most snakes, they are good at picking up olfactory cues.
      However, getting field data on exactly what they do would be very difficult. Neonate garter snakes are really small; you couldn’t use radiotelemetry.

      1. It’s my understanding that the juveniles do overwinter in the marshes in their first year. Given the snow cover and quantity of marsh vegetation, they might not freeze, or they might have natural antifreezes like some frogs do that protect against modest freezing.
        There are other hibernacula throughout the interlake; but Narcisse is the largest and most well known. The farthest north I know of is on Matheson Island in Lake Winnipeg.
        Vehicle traffic on highway 17 was a major source of mortality for the snakes as they bask on the pavement in spring and fall. Many miles of ‘snake fence’ (approximately foot high fine mesh screen)were installed and tunnels bored under the highway to restrict access to the road and give safe routes from the dens to the marshes. The efforts greatly reduced mortality, although maintenance is always a problem. Small scale conservation that actually works. The local attitude has mostly gone from ‘swerve to hit em’ to ‘swerve to avoid em’.

  5. In NY, I see just a few of these every spring crossing my lawn. I wonder if they have group dens around here?

    “Evolution is a cruel process…God doesn’t like females”
    No? But the females seem to get all the nooky they want. Seems to me things balance out in the end.

  6. As soon as I stepped out of my car, I could hear the snakes slithering in the grass, the sound was constant. I was still a 10 minute walk from the dens.

  7. David Attenborough covered this in his BBC life series.

    Some males mimic females and other males try to court them. The non-mimic males come out of hibernation first and spend time exposed on rocky surfaces to get heat from the sun. This exposes them to predation.

    The mimic males wake later and steal body heat from the courting behaviour of the non-mimic males.


  8. misogyny notwithstanding, I liked the fact that the males are not violent in their competition to mate

  9. It is hard to read this post and not speculate. In the spring, do the snakes that slither farthest away have more food (fewer other snakes to compete with), become better fed, and grow bigger? Is this negatively compensated by greater risks of not finding the way back or falling to a predator or accident along the way? Do females, because they are bigger and must eat more, travel farther than males? Or do they travel less so that surviving 1½ year-old offspring have a better chance of finding dens? Do young snakes freeze solid during their first winter?

    The video (at 2:25) is a little misleading when it states that males of other species, under conditions of sexual competition similar to that of garter snakes, have (evolved) dominance hierarchies, fight for mates, or defend mating territories against rivals. Like hummingbirds warding off competitors from flower patches or feeders (see the preceding post), fighting and territoriality can only evolve (by n.s.) when it is ‘economically viable’ to defend the ‘resource’. A territorial male garter snake in the situation depicted in the video (even if territorial behavior were to repeatedly arise through mutation) would have no chance to defend and mate with a female against dozens of sex-craved rivals. Fighting and territorial defense would simply not work. In many cases, knowing the adaptive context helps make evolutionary sense of what is going on, at least in broad outline.

  10. Well, it’s not Winnipeg exactly. It’s near Narcisse in what’s called the Interlake, between two very large lakes, Winnipeg and Manitoba. As a kid, I used to see garter snakes all the time; would pick them up and stroke them. They were gentle and non-aggressive, but always glad to be away when let go.

  11. I’ve seen massive amounts of garter snakes like this. There is even a picture of me with my dad holding a bunch of them somewhere in northern Ontario when I was about 4.

  12. Seeing the link to National Geographic, I assumed it would be to the classic November 1975 article (one of the triggers for my obsession-turned-career with snakes).

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