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Giant Ichneumon Wasp

Megarhyssa atrata


Large, thin-bodied wasp. Females are very dark black and yellow. They are parasitoids of wood-boring insects in dead, deciduous trees.


Deciduous forests in eastern North America. I spotted this one at Kent Falls State Park - drilling into a maple tree. I was lucky enough to spot this wasp just as she was getting started, and I stood there for nearly an hour watching this amazing process.


They can parasitize larvae burrowed up to 140 mm in hardwood! A membranous pouch at the abdomen's tip holds the ovipositor while the female lays eggs. When a female is ready to oviposit her eggs, she rotates segments 8 and 9 of her abdomen and unfolds her intersegmentary membranes so that they form a disc 2 cm in diameter. The surface of this disc produces a secretion that disintegrates the wooden substrate and facilitates her ability to insert her ovipositor. After she lays her eggs on the surface of the host larva she completes the same rotational movements to remove her ovipositor from the wood and the stylus returns to its resting position. This entire process takes an hour.

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32 Comments (1–25)

Christine Y.
Christine Y. a year ago

Thanks Felix!

Felix Fleck
Felix Fleck a year ago

Belated congrats! Great series.

Christine Y.
Christine Y. a year ago

Thank you Polilla!

Christine Y.
Christine Y. a year ago

Thanks everyone!

Mark Ridgway
Mark Ridgway a year ago

Congratulations !!

awesome find Christine,great spotting,congrats on the weoel deserved SOTW and thanks for sharingand thanks for sharing

DanielePralong a year ago

Congratulations Christine, this amazing and well documented spotting has been voted Spotting of the Week!

"Discover a Giant Ichneumon Wasp (Megarhyssa atrata) laying her eggs in our Spotting of the Week! These large, thin-bodied wasps are parasitoids of wood-boring insect larvae. Female Megarhyssa atrata have an an extremely long ovipositor (the tubular organ through which she deposits her eggs). A membranous pouch which can be seen at the abdomen's tip stabilizes the ovipositor while the wood surface is being drilled and the wasp lays eggs into the larvae. Project Noah member Christine Young watched this entire process which takes nearly an hour to complete due to the length of the ovipositor. Find out more about this amazing process here:".



Christine Y.
Christine Y. a year ago

Thanks Hema! Your weasel is unique and super cute :)

Hema a year ago

Christine,superb! SOTW for sure.Amazing!

Christine Y.
Christine Y. a year ago

Thanks staccyh and Leuba!

Leuba Ridgway
Leuba Ridgway a year ago

Great series and thanks for the information Christine !

staccyh a year ago

Awesome find and great photos!

Christine Y.
Christine Y. a year ago

Thank you for the nomination!

AshleyT a year ago

Your spotting has been nominated for the Spotting of the Week. The winner will be chosen by the Project Noah Rangers based on a combination of factors including: uniqueness of the shot, status of the organism (for example, rare or endangered), quality of the information provided in the habitat and description sections. There is a subjective element, of course; the spotting with the highest number of Ranger votes is chosen. Congratulations on being nominated!

Christine Y.
Christine Y. a year ago

Thanks! It was definitely one of the coolest things I've seen.

Druenn a year ago


Christine Y.
Christine Y. 4 years ago

Thanks sunnyjosef!

sunnyjosef 4 years ago

Beautiful spotting!!

Christine Y.
Christine Y. 4 years ago

Thanks Tiz! It was so amazing to watch this process!

Tiz 4 years ago

Whaat a spectacular bug and great first photo and series!

Christine Y.
Christine Y. 4 years ago

Thanks drP!

drP 5 years ago

Wow. This is a fantastic series!

Christine Y.
Christine Y. 5 years ago

Thanks Mark Ridgway!

Mark Ridgway
Mark Ridgway 5 years ago

Extraordinary series !

Christine Y.
Christine Y. 5 years ago

Thanks LorraineDianeLafleur!

Connecticut, USA

Lat: 41.72, Long: -73.48

Spotted on Jun 8, 2013
Submitted on Jun 8, 2013

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