A very large black wasp with bright yellow head and antennae. The legs are pale yellow. The body of the female is approximately 1 1/2 inches. She has a very long (3 inches) ovipositor that is often mistaken for a stinger. Her antennae are approximately 1 inch in length.
There is not much information on their status in Fontenelle Forest and Neale Woods. Females have been seen in Fontenelle Forest on low vegetation and fallen logs in mid-May and mid-July to mid-August.
These giant ichneumons are beneficial insects that prey on wood borers. They do not sting. The females use their antennae to “feel” vibrations made by Horntail Wasp larvae inside the tree. When she locates a larva, she drills into the tree with her ovipositor. When she senses the tip is in contact with the host larva, she ejects an egg and deposits it on the larva. After the egg hatches, the young Ichneumon larva feeds on the Horntail larva and pupates in the wood. When mature, it chews its way out and begins life as an adult wasp. Males are attracted to the “wood chewing” vibrations and many can be gathered around waiting to mate with the emerging female. Three species of Megarhyssa prey on the same species and all 3 could be in the tree at the same time as each species has a different length of ovipositor and can feed at different depths. Consequently, when females are about to emerge, males of all 3 species (atrata, greenei, macrurus) could be waiting on the tree.
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