[2] This is a genus of holometabolous insects within subfamily Rhyssinae that includes 37 species and belongs to Ichneumonidae, the family of wasps with the highest biodiversity in the world.

M. nortori has been introduced to South Africa, Australia, and New Zealand as a biological control agent.

[3] Both sexes can be distinguished because females have an extremely slender, and long organ to lay eggs called the ovipositor.

The species M. atrata (Fabricius) shows a bright yellow head, and an almost completely black body.

In the Neartic, Paleartic, and Australian regions, some Megarhyssa species such as M. emarginatoria, M. jezoensis, and M. nortori are known to parasitize Siricidae.

The ovipositor of M. atrata is known to puncture up to 14 cm inside the wood, and such length makes this wasp the largest species in Hymenoptera order.

[15] The reproductive cycle of Megarhyssa begins with the female locating a larva of Tremex columba inside the bark of a tree.

Once they locate a host, females must pierce the bark of trees using the ovipositor to reach the larva.

The wasps always follow a very straight line without deviating to reach the chamber where the larva lies.

[18] The movement that flight makes possible for parasitoids is crucial to reproduce, so it is related directly with fitness.

It is thought this is because females are the individuals that reach new habitats, redistribute the progeny, and locate hosts.