Banded Alder Borer

I live in Southern California and encountered the most hideous insect I have ever seen.
Here’s a description:
Black with white covering entire body.
Length: 2-3″
Antennae: very long 2″minimum
It resembled a skeleton.
Had 4-6 legs.
Body seemed very hard.
Please advise
—Peter DiVincenzo

Dear Peter,
My original guess would have been a Eucalyptus Tree Borer (Phoracantha semipunctata) but the black and white coloring suggests a relative, the Banded Alder Borer (Rosalia funebris) instead. This is a very attractive beetle with black and white striped antennae which are longer than the body. It feeds on alder, ash and other hardwood trees, occasionally boring into the wood of laurel, live oak and eucalyptus as well. Adults are sometimes attracted to the fumes of fresh paint.

Try these sites for a photo and more information.

15 thoughts on “Banded Alder Borer”

  1. We just found one of these in some older logs in our field. We took pictures but can’t get them to post here.
    We live near Port Orchard, Wa.

  2. I’ve lived on the same forested property for 25 years and never seen one. Some 6 weeks ago, I felled a dozen Doug Fir & Western Red Cedar. Today I found one of these (Banded Alder Borer) on my deck.
    As far as the “fresh paint” smell as an attractant: Fresh paint can smell remarkably similar to fresh-cut wood (especially cedar). Perhaps it gives off a similar chemical. I’m not sure that’s the answer, but that’s the truth.

  3. Great to know what it is! I just found one in Campbell River, B.C.
    on Vancouver Island. I was surprised to hear British Columbia is part of their territory. I have lived here all my life and have never
    seen one before.

  4. first hint its a borer was the large amounts of sap dripping from a 10 in dia alder.
    Another alder same age next to it was also infested with them. Cut both trees
    down and just today discover another alder infested. This one very large,
    perhaps 40-60 years old. Again the sap drippings on the ground under the alder
    was first evidence of this critter being what its named after. However these
    are living alder, not dead. So must be different than what was described in
    above article. We’ve found a dead beetle (as described in article) near both
    trees. This location is North Kitsap County, west of Seattle, Washington.

  5. I am in Tulsa, OK and I have one of these roaming outside my house. Smaller than that one put probably the size of two fingers.

    From a quick search, I’ve never heard of these as far this east as Oklahoma.


  6. Have one in vegetable garden.
    We’re in Sonoma County, California. We have a few downed oak limbs and some old wood stacked. Spectacular!


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