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The Carletonian

The Carletonian

The Carletonian

Arb Notes: Look out for wolf spiders!

< Term approaching, it’s time to review your hibernation strategies. While we hole up in heated buildings, the burrowing wolf spider digs a den below the frost line to protect herself from the snow and cold.

We found the den of a burrowing wolf spider on last week’s trip to McKnight prairie, a virgin prairie fragment owned by the College. Her burrow is visible; a “turret”- a cylinder of web and sand an inch high, and an inch in diameter (the spider herself is about 2.5 inches long, approximately the length of your thumb). A mound of sand, brought from a patch farther down the slope hill, provides an arena on which the spider fans out her web.

At night, she spreads a web along the ground and sits in the center of the webbing with her feet on the edge of the burrow, to sense the vibration of invertebrates crossing the web. Feeling the vibration, she strikes quickly, bites the insect or grasshopper with venom, and attaches a piece of web to its body. As the insect flees into the surrounding grass or attempts to fly away, the spider unreels the web. After she senses it has died of the venom, she uses her string to pull it back to her for a meal.

Burrowing wolf spiders inhabit only native prairies and dunes. (Prairies have a wide range of soil types, and well-drained patches like the top of the hill on McKnight, have desert-like sand and cacti).  Sand is brought up to form the top of the mound in a little sling of web that the spider creates. Often the sand is still wrapped in web, but this particular spider had likely eaten the web to recycle it. Imagined from the spider’s viewpoint, this is a trip up a mountain, thickly forested with stalks of grass and shrubs that on human scale would be at least one hundred feet high.

Spiders burrow to protect themselves from the Minnesota winter. They dig below the frost line, where they hibernate. This particular burrow was about six inches deep, but in colder places they reach to three feet.

The spider kills the male after mating, and spins an egg sac that she attaches to her back. After they hatch, the young continue to be carried around for their safety. Once they reach maturity, they spin web “balloons” that carry them in the wind to a place where they establish their own nests.

Almost all land in Minnesota is now inhospitable to these spiders- if ballooning spiders land on asphalt of roads or parking lots, or in a subdivision, they can’t build a burrow. Next election day, I hope preserving open space will have a place on the ballot!

-Emma Rapperport ‘13 for the Cole Student Naturalists

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