Megarhyssa macrurus

Megarhyssa macrurus, also known as the long-tailed giant ichneumonid wasp^[1] or long-tailed giant ichneumon wasp,^[2] is a species of large ichneumon wasp.^[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.

Megarhyssa macrurus
Pair of females, with individual at left ovipositing
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Ichneumonidae
Subfamily:	Rhyssinae
Genus:	Megarhyssa
Species:	M. macrurus
Binomial name
Megarhyssa macrurus (Linnaeus, 1771)

Etymology

The specific epithet of macrurus is from the Greek words makrós (μακρός) meaning "long", and oùrá (οὐρά) meaning tail.^[4]

Description

Megarhyssa macrurus has a reddish-brown body of up to 2 inches (51 mm) long.^[5] It has black and yellow-orange stripes.^[6] Its wings are transparent and the body elongated. The body and ovipositor together can be more than 5 inches (130 mm) long in the female. Males are smaller and have no ovipositor.^[6]

The ovipositor

The ovipositor looks like a single filament, but it comprises three filaments, the middle one of which is the actual ovipositor, which is capable of drilling into wood. This central filament also appears to be a single filament, but is made of two parts, with a cutting edge at the tip. The two parts interlock and slide against each other.

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]

Distribution

M. macrurus is found across the eastern half of the United States, reaching into the extreme south of Canada near the Great Lakes.^[7]

Behaviour

Pigeon tremex horntail (Tremex columba)

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.^[9] Female Megarhyssa macrurus are able to detect these larvae through the bark; they paralyse them and lay their eggs on the living but paralysed larva; within a couple of weeks the Megarhyssa larvae will have consumed their host and pupate, emerging as an adult the following summer.^[6]

Subspecies

Subspecies include:^[10][11]

• M. m. icterosticta Michener, 1939
• M. m. lunator (Fabricius, 1781) - considered a synonym of M. m. macrurus by Carlson (1979)^[10][12]
• M. m. macrurus (Linnaeus, 1771)