Saturday, September 18, 2010

Locust Borer

This pretty yellow and black longhorn beetle is the Locust Borer (Megacyllene robiniae), they are serious pests of Black Locust trees and are found throughout most of the United States. Each autumn females will lay eggs in the Black Locust trees, those eggs hatch and the resulting larvae will overwinter under the bark of the trees. In the spring they become active as the temperatures begin to rise, and they will tunnel into the trees. Often times these tunnels are up to 4 inches in depth, and the constant feeding of these grubs may kill trees that are already stressed or weakened. In areas where these beetles are prevalent the damage to stands of Locust Trees may be severe.

 (Locust Borer)

There are other Black and Yellow Longhorns, namely the Hickory Borer. The Hickory Borer is active during the spring, whereas the Locust Borer is active in the fall. Be able to identify your trees also, this will go a long way in determining which beetle you are looking at. Locust Borers are associated with the Black Locust and its cultivars, the Hickory Borer is associated with Hickory and Pecan Trees.

These are not a large beetle, the females measure up to 3/4 of an inch, males are smaller at approximately 1/2 inch. Look for them now in areas where goldenrod is in bloom. The adults are nectar feeds and go bonkers over goldenrod. I photographed these beetles at my husbands uncles place. His farm has numerous black locust trees and the goldenrod is everywhere. Which happens to provide the perfect habitat for these beetles, and I must say they were everywhere. Gauging by the activity in the following picture, their numbers won't soon decline either.


  1. Can you see an entry hole where they go in?Black Locust flowers were often eaten as a sweet treat by early settlers.

  2. I don't believe you would see the "entry" hole just because the eggs are laid behind the bark. I would say the "exit" hole would be visible in the fall as they leave their woody home though. I had heard you could eat Black Locust Blossoms, but I have not tried them yet. I will try to do so next spring.

  3. "Pest" is a relative term, since black locust itself is a rather invasive and weedy tree species. Why anyone would buy and plant this tree is beyond me.

    In addition to the hickory borer, we have a third species in the genus, the Amorpha borer (Megacyllene decora). It is also out during the fall, and you can find it at Big Lake State Park. It is somewhat bigger than the locust borer with wider yellow markings - quite attractive. You should go look for it (then post pictures (which you credit me for urging you to take :))).

  4. uh hmmm.....I take it you aren't a fan of the Black Locust tree Ted...LOL
    My husband and his whole family love that particular tree, they say it is one of the best burning cut firewood species there is. Lord knows they cut a ton of them down. I don't have an opinion one way or the other about them, but I do like how the blossoms smell in the spring. I've heard they are tasty too.

    Thanks for the info.....
    I would love to find the other borer you are talking about, and Big Lake is only about 40 minutes or so from where I live. Is it also attracted to nectar like the Black Locust Borer? Is there a certain place I would find it up there? I will definitely give you credit for the info....LOL

  5. Megacyllene decora can also be found on goldenrod flowers growing near stands of the host plant Amorpha.

  6. I just looked up that species...WOW....what a great looking beetle. I've not seen anything like that one before, and you say it is around here?

  7. i found one of those beetles flying in my house this morning

  8. I have just come to find about 100 of these beetles on the side of my car lot concrete/stone building, what do I need to do to get rid of them or get them to move elsewhere???

  9. I was called to my auto lot to find about 100 of these bugs on my concrete/stone building, how do I get rid of them or get them to move elsewhere??

    1. There really isn't anything you can do but spray for them. I would however recommend leaving them be, they are harmless and should leave on their own soon.