The disturbing habits of the stump stabber

  • By Sharon Wootton
  • Friday, August 17, 2012 1:39pm
  • Life

The female stump stabber came into the house through an open door, immediately exploring escape routes and ramming the glass, frantic to get back to familiar territory: dead and dying trees.

Stump stabbers are members of the very large family Ichneumonidae in the insect order Hymenoptera, and are more commonly called ichneumon wasps.

Think long, thin legs similar to a daddy long-legs spider, thin waist, a relatively long, thick abdomen and its signature part in females: a very long ovipositor that can be mistaken for a stinger.

Most Ichneumon female wasps also have a signature behavior.

Author John Acorn writes about one species in “Bugs of Washington and Oregon”: “The female stump stabber flies from tree trunk to tree trunk, all the while rapidly drumming its antennae while running around on the bark, quite obviously looking for something.

Then she stops. Somehow, she has detected a wood-boring grub.”

Males have a similar behavior, except they are searching for emerging females with which to mate.

Now comes the hard part.

The stump stabber forces her long appendage into, and through, the bark.

Once she is in a larva or pupa, she uses the ovipositor like a syringe, forcing an egg into the grub.

How do you get a skinny appendage through bark? Researchers are working on an answer.

Here comes the grisly part: The egg hatches and the Ichneumon grub eats its victim, keeping its food source alive as long as possible by saving vital organs until the end.

This culinary approach disturbed Charles Darwin, challenging his belief in a kind Creator.

Eventually an adult emerges, using the wood-boring grub’s tunnel or chewing its way out.

Take a hike

Take your pick: Enjoy a 90-minute walk in Mount Baker-Snoqualmie National Forest with a Forest Service guide who will talk about the area’s history as you enjoy the scenery.

The choices are:

Gold Creek Pond: Walk along a 1-mile trail of asphalt and boardwalk in sight of mountain peaks. Learn about a beaver den, ant hills and rare fish at 10 a.m. and 1 p.m. Saturdays through Sept. 2.

Twin Lakes: Hike 2 miles along Gold Creek to an old-growth forest and Twin Lakes at 10 a.m. and 1 p.m. Sundays through Sept. 3.

Reserve your spot by calling 425-434-6111 8:30 a.m. to 3:30 p.m. Thursday through Sunday.

Ask for directions to the starting point and what to bring. A $10 per person donation is suggested.

Columnist Sharon Wootton can be reached at 360-468-3964 or

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