Giant Ichneumon Wasps Ovipositing

Giant Ichneumon Wasp - Megarhyssa sp.
Female wasps ovipositing (laying eggs)
Live adult wasps photographed at Winfield IL USA, May 2005.

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Female searches for host by feeling
vibrations with her antennae.

This female wasp felt around for 10
minutes before beginnning to drill.

Wasps uses a tapping motion
with its antennae

I hit the jackpot one day (May 28, 2005, to be exact) - this one 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 (wasp, you cur). 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 macro - photography. I thrice caught them in the act of depositing eggs deep inside a dead, fallen tree.

	This series of pictures shows the female wasp drilling into wood with her ovipositor. My camera clock says the whole process of inserting the ovipositor, laying the egg and retracting took a little over four minutes.
	This wasp has chosen to insert her ovipositor into an existing emergence hole.
	Giant ichneumon wasps of both sexes will wander over the surface of logs or tree trunks, tapping with their antennae. Each sex does so for a different reason; females are 'listening' for wood boring larvae of the horntail wasps (hymenopteran family Siricidae) upon which to lay eggs, males are listening for newly emerging females with which to mate. The female wasp pictured above spent upwards of 10 minutes feeling around before beginning to drill her ovipositor into the wood. I estimate this insect at 100 - 110mm long, more than half consisting of ovipositor. The ovipositor itself consists of a hollow central tube through which the eggs are passed, and two slender 'guides' which separate from the tube and form two expanding loops on either side of the abdomen as drilling progresses. You can see these loops in the following series of images.
	Megarhyssa drilling into living tree trunk [visit the male Megarhyssa]

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.

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