Insect Quiz June, 2005

June Quiz 2005

You are walking in the park one fine sunny afternoon when you notice a really large wasp-like insect on the trunk of a maple.  The insect is well over one inch in length with a really long ‘tail’ that seems to be stabbing the tree. 

1. What is this insect?

This insect is a type of parasitic wasp known as an ichneumonid (ich‑new‑MON‑id).  This is the most numerous group of insects in the U.S. with over 3,000 species known.  However, most ichneumonids are generally not very conspicuous.  This particular ichneumonid is called Megarhyssa (meg‑a‑RISS‑a).  Megarhyssa is a reddish brown and yellow insect with a body length of about one and half inches long.  It possess an ovipositor (an egg laying apparatus) attached to tip of its  abdomen that is another two to three and a half inches long!  If you examine the ovipositor carefully, you will also notice it also has a sheath on either side of it.

2. What is its interest with the tree?

Ichneumonid wasps are parasites of other insects.  Megarhyssa parasitzes horntails, a wasp-like insect that attacks dying or recently dead hardwoods, such as oak, maple, birch, and elm.  With her long ovipositor, Megarhyssa can drill 1/2 inch or more into the wood to deliver an egg into the horntail larva.  That egg hatches into a worm-like insect which slowly feeds on the horntail, eventually killing it.  After the larva matures into an adult wasp, it emerges from the wood.

3. Is this insect dangerous to people?

Despite her large size and her menacing ovipositor, Megarhyssa, as well as other ichneumonid wasps, pose no threat to people.  She is not aggressive towards humans and avoids us when possible.  She potentially could jab a person with her ovipositor in an effort to escape if she was threatened but she would only inflict a minor wound at best.  Some people that are allergic to bees are worried that this insect may cause a severe reaction.  However, its ovipositor does not possess venom like a stinger and it is not dangerous to people that are sensitive to stings.

4. What is the best way to deal with this insect?

If you see a Megarhyssa, just ignore it.  If you find one on your property, it will go away on its own in a short time.  There are no circumstances that justify killing it or treating one with an insecticide.