[3] It is a parasitoid, notable for its extremely long ovipositor which it uses to deposit an egg into a tunnel in dead wood bored by its host, the larva of a similarly large species of horntail.

Although very thin, the ovipositor is a tube and the egg being laid moves down a minute channel in its center.

The outer two filaments are sheaths which protect the ovipositor; they arc out to the sides during egg-laying.

[6] M. macrurus is found across the eastern half of the United States, reaching into the extreme south of Canada near the Great Lakes.

[7] M. macrurus is harmless to humans;[6][8] they are parasitoids on the larvae of the pigeon horntail (Tremex columba, Symphyta), which bore tunnels in decaying wood.