What's eating our wooden raised beds?

July 16, 2022 1:24 PM

I just found a pile of sawdust at the base of a raised planting bed made of railroad ties in our backyard. Help me identify the pests and what to do now.

This is in Seattle, WA, and appeared in the past week or so - I haven't seen any previous signs of anything like this.

More photos.

There's also a soft raised pile of dirt, about 8" square, about 10 feet from the raised bed - seems like an anthill maybe? It's a bit squished - I stepped on it to see how firm it was, and it's quite soft; that area was just grass a week ago. Possibly unrelated, but would definitely be a coincidence if so.

posted by Special Agent Dale Cooper to Home & Garden (4 answers total)

When we saw stuff like that around one of the raised beds in our community garden, someone said it was either a carpenter ant or a carpenter wasp.
posted by EmpressCallipygos at 1:34 PM on July 16, 2022 [1 favorite]

Looks like carpenter ants for the wood, and moles making the dirt piles in the garden. Both very common in Seattle. I don't have any management suggestions, I have always just lived with them as they don't cause that much trouble and moles can be beneficial for your yard.

You should keep an eye out for carpenter ant sawdust or winged adults in your home though, especially if it's older and built with solid timbers.
posted by Maude_the_destroyer at 2:15 PM on July 16, 2022 [1 favorite]

I was going to say carpenter ants or drywood termites. Your planting bed of old railroad ties is similar to something I had in my backyard, down here in San Diego. Termites found a home there. They loved it. Being a gardener, I have a hard time being angry at insects. They just do what they do and we have to deal with it.
posted by SPrintF at 5:19 PM on July 16, 2022

Agree with above. To deal, put a thick line of diatomaceous earth on the ground around the perimeter of the beds, which will kill them if they walk over it. It is safe for people and pets once placed, but wear a mask so you don't breathe in the dust as you're putting it down. You can also sprinkle cinnamon, or use eucalyptus or lemon essential oils to deter them (citrus oils work for wasps/bees as well). Borax or baking soda mixed with powdered sugar is a good bait plus poison. Borax is safe for humans (at least those old enough to know not to eat it) but not pets. It will also kill any grass/other plants where you put it down, so if you go that route you'll need to be strategic about it, and especially don't put it in the beds themselves.

If it's bees, you'll see boreholes about 1/2" wide all over the place. Spray these with WD40 or vinegar to kill bees and larvae. If that's not appealing, get a Carpenter bee house and put it away from your house and beds, and just use citrus oil to deter them. You'll have to reapply it at least weekly. If you can't smell it from a few inches away, put more on. Good luck!
posted by ananci at 8:17 AM on July 17, 2022