Subject: Is this a Cottonwood Beetle?
Geographic location of the bug: AZ Tucson
Time: 07:56 PM EDT
Your letter to the bugman: I found this bug on my bar which I had the top replaced with a large Mesquite slab. This the second one I’ve found. There was a lot of small wood chips and sawdust falling out of holes. I was worried it was termites.
How you want your letter signed: Mason
Based on this BugGuide image, this is a Bark Gnawing Beetle in the genus Temnoscheila. BugGuide does not describe the food preferences in its genus page, but of the family Trogossitidae, BugGuide notes: “Many are predatory on other beetles and their larvae.” Myrmecos states: “Previously I’d encountered Temnoscheila only under the bark of dead trees, where they apparently prey on the larvae of other beetles.” We have not located any information on the larvae, and we can speculate that if the larvae are also predatory on wood boring beetles, the two individuals you found may have emerged after spending their larval stages feeding in the mesquite slab, and they emerged after metamorphosis.