What to do about burrowing beetles in deck joists?
I've got a house in Crestline, CA (at 5500 feet we have lots of pine trees and oaks) and I was digging out pockets of dryrotted wood in the joists beneath our deck when I noticed a tunnel filled with tiny pellets. I used a chisel to follow the tunnel and found a tiny rust colored beetle exactly 4mm long. I've got a bunch of pictures here:
Can anyone tell me what this beetle is? Do I need to worry about them doing any serious damage?
I didn't find any exit holes (which should be at least 2mm around and fairly noticable), and their burrows seemed to stick near the top surface of the joist (found none heading deeper into the wood) so I think they're staying near the moisture, which should keep the damage limited, especially after I add wood rot repair fluid and fill with epoxy wood. The house has been around since 1985 so I don't think the beetles are holdovers from live trees.
By carefully chiselling and tracing the tunnel it looks like it entered from the surface as something almost microscopic (probably an egg laid in a crack) and ate its way into the wood. The tunnel gradually widens and its waste pellets grow as the tunnel widens. The tunnel is filled full with the pellets, and they are loose and grainy, not sticky or fine. The tunnel I mapped was about 8 inches long with a few short branches although I think it doubled back through some dryrotted wood I'd pulled out. It had eaten through both dryrotted wood and healthy wood, but I'm hoping it's something that only really gets in originally because of the dryrot. The wood was painted where the tunnel started but there could have been a crack in the paint.
I was also hoping it was a freak thing but I found 3 more of them in another joist while digging out dryrotted areas. The first beetle I found is featured in most of the pictures and was still alive, but it barely moves (just wiggles its legs a little but doesn't crawl away or fly). A beetle I found later was also 4mm but had longer legs that looked more appropriate for crawling outside a tunnel. It appears in the first picture. The last two pictures show a beetle amongst its pellets and a few pictures have a dime for scale.
I've found quite a lot of beetles online that look similar but it's hard to be sure which one it is, if any.
Thanks for reading and I hope this is nothing I need to worry too much about.