The female of this species of giant Ichneumon is about 1 1/2 inches in length not including antennae and ovipositor. The ovipositor is black, threadlike and approximately 2 inches long. The head and thorax are red, as is the abdomen. The abdomen has transverse bands of black and pale yellow stripes. The legs are red. Wings are a tan color with a triangular black mark on the leading edge of the forewing near the tip. The antennae are long, slender and black. The male (photos 4, 5 & 7) is approximately 1 – 1 1/2 inches in length. His abdomen is long and black to dark red. The thorax is black with yellow markings. The legs are mostly yellow.
This giant ichneumon is thought to be uncommon in Fontenelle Forest and Neale Woods. Females and males can be found on dead or dying tree trunks. It has been seen in Fontenelle Forest in late April and mid-September.
This giant Ichneumon is in the subfamily Ryssinae. They are beneficial insects that prey on wood borers. The adults don’t feed and 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, macruruus) could be waiting on the tree.
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