Megarhyssa inserts a remarkably long “tail” into a tree to deposit an egg on an unsuspecting host.
Chilly temperatures and snowy weather create conditions unfavorable for hunting and photographing bugs in the wilds of Maryland. Over the next several weeks, Bug of the Week will delve into our files and answer questions sent by bug aficionados. This week’s fantastic creature comes from New Jersey where a Bug of the Week fan observed a scary wasp perched on a window. The curious feature of this beauty was a “tail” that greatly exceeded the length of the rest of the wasp’s body. The insect itself was about an inch and a half but the tail was more than three inches long. The tail is called an ovipositor. This deadly lady is Megarhyssa, a member of a group of insects called ichneumon wasps and a relative of wasps we visited in the episode entitled “Parasites at the porch light – Ichneumonid wasps”.
A female plans her escape to the outdoors.
The female Megarhyssa uses sophisticated chemical receptors to locate a log or stump infested with another member of her clan called a wood wasp. The larva of the wood wasp bores deep into the tree where it consumes plant tissues. Once Megarhyssa has located an infested tree, she lands on the bark, and inserts her amazing ovipositor, full length, into the wood. This appendage enables Megarhyssa to deliver an egg to the body of its victim. The egg hatches and the larva of Megarhyssa consumes the developing wood wasp. After completing development, the fully grown Megarhyssa larva turns into a pupa within the gallery of its host. After emerging from the pupal case, the adult uses powerful jaws to chew its way through the wood to the bark of the tree where it emerges.
Male Megarhyssacomplete development rapidly and emerge before the females. They are sometimes seen clustering on the bark of trees waiting for the ladies to appear. Scientists observed several species of Megarhyssa emerging from a single tree and wondered why many closely related species could be found sharing what appeared to be the same resource. Careful observation revealed that each unique species of Megarhyssa had an ovipositor of slightly different length. This enabled short-tailed species to utilize prey just below the bark while long-tailed species attacked wood wasps deep within the tree.
References
Special thanks to Karina for sharing her image and providing the inspiration for this episode. The fascinating study, Ecology of three sympatric species of parasitic insects in the genusMegarhyssa(Hymenoptera: Ichneumonidae) by Harold Heatwole and Donald M. Davis, was used as a reference of this episode. To learn more aboutMegarhyssa, please visit the following web site.