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The Loom
« Hornet, Hardcore [Science Tattoo]
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The Cretaceous Comes To My Front Yard

walking turtle600Sunday morning was cool and foggy, and so we were not surprised to discover the garden full of craters and trenches. A snapping turtle the size of a manhole cover was busy laying her eggs.

This is an annual ritual in this part of New England. The first time I encountered a snapping turtle here, not long after we had moved into our house, I was terrified. Our children were toddlers, old enough to run but not old enough to know they should stay away from animals that can snap off your finger. Somehow I had to get the turtle out of my yard and back into the creek that runs behind our house. With no experience in turtle-wrangling, I decided to get a broomstick. I tapped the turtle on its shell, to signal that I wanted it to leave. It looked up at me with supreme indifference.

My helplessness made me hallucinate. I feared the turtle was going to break into the house somehow and eat our cats. I called our town’s animal control line, and ended up talking to a policeman. He gave me a suprisingly detailed lecture on the natural history of the snapping turtle. On cool, foggy mornings in late spring, he explained, females emerge from streams and wetlands to bury their eggs in the soft earth. They take care of their business in about an hour, and then they leave. He would not be coming to my house to rescue us.

He was right. The turtle picked a lush bed of mulch and mud, near a rose bush, and laid her eggs. I stared at from the front door with my children until we got bored. When I checked back a few minutes later, it was gone. I never realized that a snapping turtle can disappear when it wants to. After a few weeks the eggs hatched. In the summer we discovered adorably vicious baby snapping turtles trying to find their way back to the water. Every spring since, the snapping turtles have returned, and we’ve gotten more comfortable with them. I don’t bother the police. Instead, we get reasonably close to the turtle to observe.

We usually get one snapping turtle visiting us each year. We’re grateful, but we also know these visits are a shadow of a former glory. One of our neighbors, who grew up in our town, remembers armies of snapping turtles swarming up out of the creek in the spring. We live in biologically impoverished times, with constipated streams, filled-in marshes, and other assaults on the habitat of turtles in New England. Snapping turtles have been wandering out of marshes for millions of years. The oldest turtle fossils are about 220 million years old, but snapping turtles evolved much later. They belong to a 90-million-year-old lineage that also gave rise to species that span the extremes of turtle biology, from tiny mud turtles to leatherback turtles, the biggest reptiles on Earth, which swim across oceans.

Laying turtle440This morning’s visitation was particularly mesmerizing, because the snapping turtle angled her body in such a way that we could see her eggs drop into the hole she had dug. They were the size and shape of eyeballs. As the eggs eased out of her cloaca, she tapped them with her right back foot into the hole, like a soccer player giving a ball the extra kick it needed to reach the goal. One after another, the eggs tumbled out. We counted a dozen, but snapping turtles can lay dozens more at a time.

They pick these nests carefully. They chose these spots for their temperatures. Like many other turtle species, snapping turtles end up male or female depending on the temperature. At low and high temperatures, they produce females; at intermediate temperatures, they make males. Snapping turtles don’t have thermometers, but they have evolved a simple rule of thumb (or claw). They seek out soft, sandy soil, which tends to be the right temperature to produce a mix of males and females.

Unfortunately, we may be setting ecological traps for the turtles. They sometimes lay eggs in yards underneath planted trees or near houses. The shadows cool the temperatures compared to sites they pick in natural habitats. On the other hand, global warming may send them in the other direction. In either case, we may cause the turtles to make too few males. And because they live so long (up to 40 years or more), they will be slow to evolve new preferences. I hope that my grandchildren will be able to come see snapping turtles rip up our garden, but I cannot be sure.

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May 24th, 2010 12:21 AM by Carl Zimmer in Evolution | 12 comments | RSS feed | Trackback >

12 Responses to “The Cretaceous Comes To My Front Yard”

  1. 1.   humble reader Says:
    May 24th, 2010 at 6:01 am

    Wonderful. As a youngster i had such an encounter of the cretaceous kind
    in New England, quite terrifying, their jaws seem able to snap your
    broomstick if provoked. Now is the time for cambrian encounters with
    horseshoe crabs if you visit the southern NE coast or further south.
    Childhood memories i should try to refresh.

  2. 2.   NewEnglandBob Says:
    May 24th, 2010 at 6:41 am

    Thanks for this educating story, Carl.

  3. 3.   Skeptical Rationalist Says:
    May 24th, 2010 at 6:53 am

    Very cool to see. Any chance you’ll give us “The Cretaceous Digs its Way Out of My Front Yard” in a few months? I’d love to see pics of the nesting site in context, and during/after the hatchlings’ emergence.

  4. 4.   MNiceLady Says:
    May 24th, 2010 at 11:40 am

    When I was a kid, I was holding one with a bikini on and it snapped my belly
    OWCH

  5. 5.   Hank Fox Says:
    May 24th, 2010 at 4:28 pm

    I pulled off the road one time to prod one out of the roadway so it wouldn’t get killed. I poked at its tail with my foot, thinking it would be sluggish, and it whipped around quick as a snake. I was shocked at how fast they are. Fortunately it was a cheap lesson — no body parts exposed, no damage done. But I have a healthy new respect for them.

  6. 6.   marcel Says:
    May 24th, 2010 at 4:31 pm

    That must have been way cool – I’ve never seen one of these wearing a bikini.

  7. 7.   Dallas Krentzel Says:
    May 24th, 2010 at 4:35 pm

    I had a snapping turtle appear in my drive way last Tuesday night. I was rather confused, because, although I live in Louisiana, there aren’t too many significantly sized bodies of water that close to my house, which is in a small suburb. I also, like you, attempted wrangle it, using a piece of cardboard to push it into a box. I then drove it about a mile away near a creek. I figured if it stayed in my neighborhood, it was bound to be killed, or would starve.

    It’s interesting to know that it was probably a female trying to lay her eggs somewhere though.

  8. 8.   Greg Peterson Says:
    May 24th, 2010 at 5:23 pm

    Great story. I love turtles. I have one in my home in an emormous tank that keeps me entertained with its antics (slow-moving antics, but still), and I always look for them on my walks. I live in Minnesota, and our 10,000 lakes usually have a bunch of turtles in them…but of course they are getting more rare here, as well. A couple of weeks ago my girlfriend found a tiny painted turtle (or red-eared slider or–I didn’t really ID it), smaller than a quarter, trying to cross the sidewalk from one body of water to another. Nothing is cuter than a baby turtle because even as miniatures of what they’ll become, they seem all grumpy and bad-ass. And ths is never more true than with snappers. I picked up a baby one a few years back near another pond, and it seemed to think it was Godzilla, but the little critter fit snuggly in the palm of my hand.

  9. 9.   Duncan Wilkins Says:
    May 24th, 2010 at 8:36 pm

    I hate to be pedantic, but I believe that the largest reptile on earth is the Salt Water Crocodile.

  10. 10.   Brian Too Says:
    May 25th, 2010 at 8:36 pm

    Turtles survived the Chicxulub event, so they have a few tricks up their, ah, shell. Have some faith in their reptile ways. All they need is for humans to not make it impossible for them to live.

  11. 11.   Jackson Says:
    May 27th, 2010 at 8:13 pm

    Every year We have these turtles crossing a busy road from wetlands to a farmer’s field this week — so dangerous.

    Once I stopped the car to help a turtle — as I lifted him up he lurched and tried to snap — I dropped him and found he still had water in his shell which splashed…

    They won’t stop trying to cross the road.

  12. 12.   mikayla Says:
    May 30th, 2010 at 8:34 am

    wow i just found a snapping turtle it wont snap i love reptiles

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