Found this at a lakehouse after about a month of not being there. No signs of holes anywhere.

That was my first guess as well.

Ya, sure looks like carpenter bee mess. There's a hole somewhere.

If you can find the hole, there is a spray that kills the larvae they leave in the hole. Assuming still there. I deal with them every year at my house. Exterior.

Look up higher on the wall above this area

Thanks all. I'll try to hunt down the hole. How big of a hole am I looking for? I did see what looked like a blue wasp around, but not sure it's related.

bigevent99 said:

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Thanks all. I'll try to hunt down the hole. How big of a hole am I looking for? I did see what looked like a blue wasp around, but not sure it's related.

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Bumblebee sized hole.

Walked right into that one

If you have spray foam insulation in your walls, that could also be a sign of Acrobat Ants chewing it up and expelling the insulation particles to create their colony.

Carpenter bees or ants are also valid culprits, as mentioned above.

Edit to add: If you pound on the wall in the vicinity of that pile, whatever is creating the pile will usually exit through the access point, or points.

If you want to eradicate them. Bifen is hell on bees. Spray the area.

Will Bifen blast aphids on my crapes?

Absolutely. Bifen will kill just about everything.