A Creepy Creature for Halloween

The other day I posted a grainy video of a long, thin worm gyrating in a peanut butter jar full of water on the North Shore Nature Program’s Facebook page.  Here’s a slightly better photo.

PictureThis animal was found in a drainage pond at the Town Forest in Groveland during a school program.  I’ve had the pleasure of exploring various wild areas in Groveland over the last few Fridays with the 4th graders of the Bagnall School.  They have a wonderful program where all the 4th-grade students spend time throughout the year exploring the town’s open spaces, learning about natural history, and performing trail maintenance and other public service projects.  It’s the type of program more schools should pursue.

But back to the worm.  We were about to head off into the woods to learn about animal signs when we noticed this weird thing squirming and dancing just below the surface of a small drainage pool.  I quickly grabbed my handy peanut butter jar and scooped it up.  The students and I spent some time guessing what it was and trying to figure out how it had arrived in this little pond; a pond that has no inflow or outflow, save for a few underground drainage culverts.  We all agreed that I should take it home and figure out what it was.

I consulted with a few references, and local expert Richard Wolneiwicz, and confirmed that it is a horsehair worm.  The one we discovered is about 10 inches long, but apparently they can grow up to 2 feet in length.  The students and I had hypothesized that perhaps it was a parasite (and therefore carried by another animal to the small pond in which it was found) and we were correct.  In fact, these worms have a fascinating life story.

The worm starts as an egg, laid by an adult, in a pool of water (usually fairly shallow and not necessarily of the highest quality).  The larvae emerge from the eggs in early spring and immediately attach themselves to vegetation near the edge of the pond.  As the high water of spring recedes, this vegetation becomes exposed to terrestrial insects like crickets, grasshoppers, katydids, and the like.  While eating this vegetation, the insect also digests some of the larvae.  And here’s where things get kind of cool (or gross depending on your temperament).

The larva feeds on the inside of the insect and continues to develop.  Once the larva reaches its adult stage, the worm continues to grow and somehow taps into the insect’s nervous system, directing it to water, often causing the insect to jump into the water (and therefore drown).  The adult worm then emerges from the insect to find a mate and reproduce.  And the cycle begins anew.

So cool!  And sort of terrifying…  I’ve been exploring nature since I was a kid and I never cease to be amazed by the complexity and coolness of the natural world.

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