The female walks the surface of a dead trunk tapping with her antennae, apparently detecting vibration and chemical traces from a wood wasp larva tunnelling within. Having located one, she raises her abdomen, braces the ovipositor in a loop above her, and begins to bore.
The ovipositor is a composite of interlocking valves that slide against one another, cutting rather than pushing, and the tips carry metal ions, including zinc, that harden the cutting edges. Drilling takes tens of minutes and can penetrate several centimetres of wood. She lays one egg on or near the host, and the larva that hatches consumes it.
The long filament trailing behind such a wasp regularly frightens people who read it as a sting. It is an egg-laying organ; Megarhyssa cannot sting. The group as a whole is enormous, with ichneumonids numbering tens of thousands of described species and probably many more undescribed, and their host specificity was one of the observations that troubled Darwin about a benevolent design of nature.