Wildlife Photography | The Mega Wasp, Megarhyssa

Megarhyssa atrata wasp photo

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When you go to school to study insects you can expect your family, friends and strangers to find it extremely odd but quickly embrace your oddity by turning to you when there is the arrival of an unwanted, 6-legged alien in their domain. Equally a fact of life when you are an entomologist is that you are often gifted  insects because those same family and friends have by now embraced your weirdness and are trying to demonstrate their support of your strange passion. Or something like that, haha.

A couple weekends ago, Josh told me he had a “nerdy present” for me. Some kind of new photography toy? No, he would have said “cool present” if that were the case. I knew right away…its a bug, isn’t it?

Sure was. There was an Ichnuemonid wasp (Megarhyssa atrata) hanging out on the garage door. They range in deciduous forests across northeastern and central North America and are ectoparasitic in order to live. An ectoparasite is an animal that lives on the outside of a host and feeds on the host in order to survive. Megarhyssa are ectoparasites of siricid woodwasps, specifically the pigeon horntail (Tremex columba) that develop as larvae in hardwood trees.

Megarhyssa atrata photo


Those big, long filaments hanging off the end of her body are the ovipositor and it’s sheath. They actually can’t sting people, so fear not, entomophobes. She uses that long ovipositor to drill into the tree to lay an egg on the larva of the woodwasp. Once her egg hatches, the Megarhyssa larva begins feeding on the woodwasp larva. All the nutrition the Megarhyssa is going to get before transforming into an adult is a result of the parasitic relationship it has with this one woodwasp larva. This relationship begins in the summer and lasts all the way through winter until the following spring when the Ichnuemonid wasp chews its way out of the tree as an adult. Maybe you are wondering how in the heck she even knows there are woodwasp larvae in the tree and how to precisely drill to lay her egg on a larva. Have you ever walked past a tree and heard a strange grinding noise? That grinding is the chewing of, most likely, pine sawyer beetle grubs eating and developing inside conifer trees. Megarhyssa use a combination of auditory (from the chewing noises) and olfactory cues to locate woodwasp larvae developing inside the trees. She uses her antennae to palpate the trunk of the tree to pick up chemical cues from frass and fungus associated with the woodwasp.

Anyway, it’s a cool insect story and now you know what kind of gifts a girl like me gets 🙂 Oh, and since there is no size reference in these pictures, you should know that she was longer than the length of my hand.

megarhyssa atrata image

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