21 June 2009

Ichneumon wasp - in the groove

The ichneumon wasp is a remarkable predator; the photos above emphasize the extraordinary size of the ovipositors. The female lays her eggs inside insect grubs that are burrowing below the bark of a tree. One can't help but be awed by her ability not only to detect the precise position of her victim, but to force the ovipositor through several inches of dense wood (to my knowledge, no one yet has explained how the latter task is achieved).

This is the creature that caused Charles Darwin to doubt the benevolence of God: "I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of Caterpillars..."

The lady above was clever enough to make her approach through a saw cut in what I believe was an oak stump; starting in that groove saved her an additional quarter inch of drilling. She was fully occupied and didn't mind my placing the camera lens right next to her for a macro view.

Photographed yesterday at the delightful Pleasant Valley Conservancy, located between Black Earth and Mt. Horeb, Wisconsin.

Both photos enlarge to fullscreen with a click.


  1. What are the two graceful loops that stick way up from her back?

  2. Those are the ovipositors! They exit from her tail, loop up in the air, then come down between her front legs where they pierce the wood. They are not always in that position - I think they stick straight back or may be retracted somehow when she's not laying eggs. I presume the arch helps her get leverage for the drilling procedure.

  3. Another amazing thing about these wasps is that they inject not only eggs, but also viruses into the grub. The viruses help the wasp larva to survive the attacks of the grub's immune system as it develops. Remarkably, these viruses are part of the wasp's genome that "pop out" and act like independent entities. It's as if part of your DNA were to become a cold virus that infected your enemies! See here: http://en.wikipedia.org/wiki/Polydnavirus

    Love the blog, keep it up!

  4. Oh, wow. I thought the ovipositors were just the things that go down into the wood; I didn't realize they were the ends of the loops. But now I can see how it works.
    Terrific photos.

    Luke, that would be very handy to have!


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