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Giant Ichneumon Wasp (Megarhyssa atrata)

Detailing the identifying qualities of the Giant Ichneumon Wasp, including physical features and territorial reach.

 Updated: 8/15/2017; Authored By Staff Writer; Content ¬©

  Giant Ichneumon Wasp  
Picture of Giant-Ichneumon-Wasp-Megarhyssa-Atrata
Picture of Giant-Ichneumon-Wasp-Megarhyssa-Atrata

Long, lean bodies of Giant Ichneumon Wasps bespeak speed, but it's the thin, bendable, needle-like ovipositor of females that make most people worry.

Wasps in the Megarhyssa genus are the largest Ichneumon wasps on the continent. There are four species in this genus and M. atrata is one of the more commonly spotted ones. Females have syringe-like ovipostors at the tip of the abdomen, which is often mistaken for a really long and threatening stinger. In truth, this ovipositor is used to lay eggs into the hard wood of tree trunks and the species does not sting people.

Females try to discern where the eggs of Horntail Wasps were laid, a shorter, robust wasp that also injects its fertilized eggs into tree trunks. It is unknown if the female follows existing cracks and holes to locate the host, or if she creates her own. The Megarhyssa atrata female places her own eggs near the Horntail eggs. The Giant Ichneumon Wasp larvae will parasitize the Horntail larvae, feeding off them as they grow. They pupate inside the tree and chew their way out to the surface. Adult males are believed to be attracted to the chewing noises and may be seen waiting for females on a tree trunk as they emerge in order to mate with her. Not all females are successful in transplanting eggs. Their large size and the egg-laying procedure make them vulnerable to predators like birds and raccoons. Sometimes, all that is left of a snatched female is her long ovipositor sticking out of the tree trunk like a whisker.

Look for M. atrata in woodlands and forests on tree trunks, especially those of dead or dying deciduous trees. They are active from spring through summer. While the larvae are known to be parasites of other wood-boring wasps, it is not known if adults feed.

Giant Ichneumon Wasp Information

Category: Bee, Ant, Wasp and Similar
Common Name: Giant Ichneumon Wasp
Scientific Name: Megarhyssa atrata

Taxonomy Hierarchy

 Arrow graphic Kingdom: Animalia
  Arrow graphic Phylum: Arthropoda
   Arrow graphic Class: Insecta
    Arrow graphic Order: Hymenoptera
     Arrow graphic Family: Ichneumonidae
      Arrow graphic Genus: Megarhyssa
       Arrow graphic Species: atrata

Size, Identifying Tags and Territorial Reach

Size (Adult, Length): Size (Adult, Length): 40 mm to 130 mm (1.56 inches to 5.07 inches)
Identifying Colors: black, yellow
Additional Descriptors: flying, stinging, needle, syringe, huge, large, big, shiny, helpful, beneficial

North American Territorial Reach (Though Not Limited To): EASTERN NORTH AMERICA ONLY: Alabama; Arkansas; Connecticut; Delaware; Florida; Georgia; Illinois; Indiana; Iowa; Kansas; Kentucky; Louisiana; Maine; Maryland; Massachusetts; Michigan; Minnesota; Mississippi; Missouri; Nebraska;New Hampshire; New Jersey; New York; North Carolina; North Dakota; Ohio; Oklahoma; Pennsylvania; Rhode Island; South Carolina; South Dakota; Tennessee; Texas; Vermont; Virginia; West Virginia; Wisconsin; British Columbia; New Brunswick; Newfoundland and Labrador; Nova Scotia; Ontario; Prince Edward Island; Quebec; Mexico

A Note About Territorial Reach: Keep in mind that an insect's reach is not limited by lines drawn on a map and therefore species may appear in areas, regions and/or states beyond those listed above. Insects are driven by environmental factors, food supplies and mating patterns and do not nescessarily work within hard-and-fast territorial lines like we humans do.

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