Whitespotted Sawyers

2013 April 10

Sam found this beetle in the living room on June 9. 2012, and was amazed by its very long antennae.

It was a pretty good-sized beetle, and the total antenna span was at least two inches.

This is certainly one of the long-horned wood-boring beetles. Based on its general appearance, and on the white spot on its “shoulder” where the wing covers come together, I think it’s a White-Spotted Sawyer, Monochamus scutellatus.

As long as its antennae are, they are only about as long as its body, which makes me think it is a female (more on this in a bit).

The jaws are pretty substantial, and look good enough to dig into wood to lay their eggs.

And, if you thought that the first beetle had long antennae, have a look a this one. It’s a male Whitespotted Sawyer that Sam caught in the yard just a couple of weeks later on June 25, 2012, and his antennae are twice as long as his body!

In addition to the longer antennae, the males also tend to lack the white speckles on their wing covers. They still have that white mark on the shoulder where their wing covers come together, though.

The male also made that kind of rasping squeak that some beetles make by rubbing their various body-armor plates together. It sounds like this:

We didn’t hear the female make this noise, I don’t know if that’s because it is a sex difference, or if the female just wasn’t sufficiently annoyed to do it.

The male also had something odd wrapped around the base of one of his antennae. I don’t know what it is. Maybe a scrap of his old pupal skin?

His antennae dominate more of his head than his eyes do. In fact, if we look at the back of his head, we can see that his eyes wrap around the antennae bases up on the back. So, basically he sees around his antennae (which would otherwise block a lot of his view) by having his eyes just extend around them.

His front feet are bigger and flatter than the female’s front feet, too. Maybe to help in holding on to her during mating?

So, these beetles mostly lay eggs in wind-damaged or fire-damaged coniferous trees like pines, firs and spruces, and the larvae burrow in. They spend a bit over a year (including two winters) tunneling in the wood, and emerge as adult beetles in their second year. They are “primary borers”, getting into the wood of still-living trees and producing tunnels that let in fungus spores and other wood-borers that finally finish off the tree. Which means that these are some of the ones that are actual forest pests, and not just incidental decomposers of wood that has already died.

If the adults are like other longhorned beetles, they are kind of omnivorous. In which case they would eat nectar, pollen, general plant leaves, fruit, fungus, and anything else that strikes their fancy.

12 Responses
  1. lessermystery permalink
    July 3, 2014

    Thank you for the excellent job in posting this. I came across one today, and boy, was it ever friendly, intelligent, and cute!!!

  2. beth permalink
    June 8, 2015

    I think I found one of these but it didn’t have any spots is that possible?

  3. June 9, 2015


    I think the only white spot that is always present in this species is the one in the middle of the back where the wing covers come together.

    There are a lot of different longhorned beetle species, and some of them are black without any white spots at all, so you may have one of them. Or, it isn’t out of the question that the white spot on the back might be absent or too small to see easily.

  4. June 10, 2015

    scary I didn’t want to get close to him I thought it was a leaf at first then it started to move I thought I was going to have a heart attake seriously I did hahahahahahahahahaha a BIG antennaeso scary.

  5. June 10, 2015

    so I have seen like three in my house and I have no idea what to do because they scare me half to death. would killing them help? why do they come into houses?

  6. June 11, 2015

    I suppose they come into the house because the woodwork smells like trees. I wouldn’t worry about them, they aren’t venomous, and the worst they might be able to do is give a small pinch. I’d just toss them outdoors.

  7. Katherine permalink
    June 24, 2015

    I woke up in the middle of the night with this in my bed, crawlung on my arm. Its horrifying when you are half asleep and can barely see. Thanks for posting this! I didn’t know what it was.

  8. Ryan Garcia permalink
    July 8, 2015

    Good to know! I work at a local mine in New Mexico where these little guys flourish. I don’t understand why, as there’s no trees. But these beetles are very resilient. They will land and walk over scorching hot, freshly welded metal w/o flinching. Kinda freaks us out (my crew and me).

  9. Paul W permalink
    July 11, 2015

    Cat was trying to catch this bug outside on back porch. If they kill trees I guess we’re suppose to dispose of him but as someone else said they seem intelligent. He made a sound when I was putting the lid on the jar. Never heard a bug talk like that before. Unnerving.

  10. Stacy S. permalink
    July 26, 2015

    My family and I just spotted one crawling on the front of my house.. It was very freaky looking and scared us a little but very interesting.. We actually got to watch it turn its head in a strange motion and eat another bug.. Glad to have been able to find this article so easily.. Great pics also!!

  11. Sabrina permalink
    July 11, 2018

    Omg so I had no idea what this was but thanks to this post I now know. R these bugs known to be aggressive? I had one in my house and if literally followed me in a circle three times. Never seen anything like it. Please lmk tia

  12. July 12, 2018

    Sabrina: They don’t seem to be particularly scared of people, but I never noticed them being aggressive or following me around, so this is new. But, even if they are aggressive, I never had any problem with being bitten. As you can see from the way I’m holding them in some of the pictures, they certainly had the opportunity to bite, and they didn’t do it.

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