Giant Ichneumon Wasps Ovipositing

Giant Ichneumon Wasp - Megarhyssa macrurus
Female wasps ovipositing (laying eggs)
Live adult wasps photographed in the wild at Winfield and Lisle, Illinois, USA..

I hit the jackpot one day (May 28, 2005 to be exact) - this half-dead tree seemed to attract these male wasps by the dozens. So I spent several hours over the course of 2 days shooting the males. Magnificent insects, to be sure, but what I really wanted was a female. I only saw a couple, and they did not hang around to pose, darnit. So I kept going back, day after day, hoping, praying to the Sylphs and Dryads that inhabit my neck of the woods to get a shot of a female... and then, oh boy! I hit the powerball lottery of insect macrophotography. I thrice caught them in the act of depositing eggs deep inside a dead, fallen tree, and once in a live, upright tree.

Giant Ichneumon Wasp - Megarhyssa macrurus
(Above and below)
This early spring wasp drilled her ovipositor into solid wood (and presumably, laid an egg onto a prey item) over the course of 4 minutes. The female wanders over the surface of the fallen log, tapping the wood with her antennae. She is "listening" for the vibrations of her prey target: a larvae of the horntail wasps, which live inside cells in the wood. This gal spent a full 10 minutes prospecting before she began to drill. At this point, her ovipositor is "fully assembled" and appears as a solid-looking threadlike structure extending fully 2 inches behind her.

Giant Ichneumon Wasp - Megarhyssa macrurus

Giant Ichneumon Wasp - Megarhyssa macrurus
As the drilling begins, the wasp raises the tip of her abdomen until the ovipositor is perpendicular to the surface, then begins pushing the tip into the wood. The abdomen sort of splits open as the two outside "guides" begin to exert pressure and separate to loop back on either side of the abdomen, to allow the abdomen to push closer to the surface.

Giant Ichneumon Wasp - Megarhyssa macrurus

Scientists are still not sure how the wasp "drills." It is thought vibration might be involved but no one is sure. I suspect the tip of the ovipositor is sharp and the wasp forces aside the "soft" tissue of the wood much as you would push a needle into cork - except the wood of living trees is much harder and denser than cork, so who knows? It's amazing, to say the least. And how does that wasp know exactly where and when the egg must be laid? For it must be laid inside the cell of the alien larvae - sometimes laid directly on the body of the prey, where it will develop and eat the host from the inside out.

The great Charles Darwin came up against one of the greatest tests of his religious faith when studying the Ichneumonidae and contemplating their seemingly evil and cruel ploy for exploiting other creatures; he thought the monstrosity too evil for God to have thought of it, much less condone it.

He wrote, in 1860, "I own that I cannot see as plainly as others do, and as I should wish to do, evidence of design and beneficence on all sides of us. There seems to me too much misery in the world. 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, or that a cat should play with mice."

Giant Ichneumon Wasp - Megarhyssa macrurus
The ovipositor is now almost fully inserted, and the abdomen has opened up like some kind of ghastly sofa-bed. The ovipositor consists of 2 "guides" and the actual ovipositor which slides in between them. The guides are the two dark thread-like arches at the left of the abdomen. The ovipositor is emerging from the very tip of the abdomen where it intersects the guide assembly. It's very difficult to tell how she's doing it while it's happening.

When the wasp senses the tip of the ovipositor in contact with the host larva, she injects the egg through the hollow tube. After the egg hatches, the young ichneumon wasp larva feeds on the horntail larva and then pupates in the wood. When mature, it chews its way out and begins life as an adult. Adult male wasps are adept at discerning wood-chewing vibrations. It is this that attracted the hoards of male wasps to this tree and log to begin with, which in turn attracted me.
Giant Ichneumon Wasp - Megarhyssa macrurus
This is a close as I got. The camera lens is about 2 inches from the wasp. I attribute her cooperativeness to a single-minded pursuit: reproduction.

Giant Ichneumon Wasp - Megarhyssa macrurus
A job well done, the wasp withdraws her ovipositor and quickly makes her escape. My camera clock shows the whole process took a litle over 4 minutes.

Video of the egg-laying process

Megarhyssa drilling into living tree trunk

Male Megharyssa wasp searchs with his antennae for emerging virgin females with which to mate.
More images of males HERE.
Read an essay by Stephen Jay Gould about the unsettling implications of ichnemuon wasps for natural theology.

Paper Wasp
Polistes dominula

Great Black Wasp
Sphex pennsylvanicus

Great Golden Digger Wasp
Sphex ichneumoneus

Bald-faced Hornet
Dolichovespula maculata

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