Physical characteristics: These large wasps measure 0.59 to 1.77 inches (15 to 45 millimeters) in length. The female ovipositor is often twice as long as the body. Some wasps measure more than 6.29 inches (130 millimeters), including the ovipositor. They are black, reddish brown, and yellow and have round yellow spots down the side of the abdomen.
Geographic range: This species is native to the United States and has been introduced into New Zealand, Tasmania, and Brazil.
Habitat: These wasps are found in pine forests and plantations.
Diet: Adult wasps drink nectar, but the larvae eat the wood-boring larvae of horntails.
Behavior and reproduction: The larvae are parasitoids on a wood-
Megarhyssa nortoni use their sharp jaws to cut sections of many kinds of green leaves and carry them back to the nest. (Illustration by Barbara Duperron. Reproduced by permission.)
boring wasp larvae. They feed inside the bodies of mature horntail larvae.
Horntails lay their eggs in pine trees and introduce a special wood-digesting fungus at the same time. The horntail larvae bore through and eat the wood that has been broken down by the fungus. The smell of the fungus attracts female Megarhyssa to trees infested with horn-tail larvae. Female Megarhyssa use their long ovipositors to bore through the wood to lay an egg on or near the horntail larvae. The parasitoid larva develops and pupates inside the body of its host.
Megarhyssa nortoni and people: Megarhyssa nortoni does not bite or sting. It has been imported into various parts of the world to help control horntail forest pests. They are sometimes used with another hymenopteran parasitoid, Ibalia leucospoides, which attacks the young horntail larvae.
Conservation status: This species is not considered endangered or threatened. ■
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