Ichneumon wasp species are highly diverse, ranging from 3 millimetres (0.12 in) to 130 mm (5.1 in) long. Most are slender, with the females of many species (particularly in the genus Megarhyssa) having an extremely long ovipositor for laying eggs. The female finds a host and lays an egg on, near, or inside the host's body^[1]. Upon hatching, the larval ichneumon feeds either externally or internally, killing the host when they themselves are ready to pupate. Despite looking formidable, the ovipositor does not deliver a sting like many wasps or bees. It can be used by the wasps to bore into and lay eggs inside rotten wood.   wiki

Megarhyssa macrurus (common name giant ichneumon wasp), is a species of large ichneumon wasp.

It is a predatory insect, notable for its extremely long ovipositor. It uses this to deposit an egg into the tunnel bored by another species of wasp, the pigeon tremex.

Its species are predatory insects. On the trunks of dead trees, they seek out the tunnels created by their natural enemy, another species of wasp, the pigeon tremex horntail (Tremex columba). Pigeon horntails are wood-borers. They tunnel into the dead wood, and deposit an egg.

Megarhyssa macrurus seeks out these tunnels. They are able to detect pigeon horntail larva through the bark of the dead or dying tree. When the female finds one, she drills into the wood to reach the larva. After laying her egg next to the larvae of the pigeon horntail, she will sting the larva, paralyzing it. The Megarhyssa macrurus larvae will then completely consume the paralyzed larva within a couple of weeks. It will then pupate and remain under the bark of the wood until the next summer, at which time it will emerge as an adult.

More info: http://www.cirrusimage.com/hymenoptera_ichneumon_megarhyssa_fem.htm

http://www.nypestpro.com/giantichneumonwasp.html

http://wiki.nisk.k12.ny.us/groups/73sciencesoron/wiki/ece38/

Is it true:

"Giant Ichneumon Wasps are carnivores. In fact, they are strict carnivores. They cannot eat plants, so they are not omnivores. When it comes to food, the Giant Ichneumon can only survive on one thing, and that’s the Horntail Wasp’s grubs, or larva. It will not be able to survive off any other food."