Are they reddish and oblong, like this?
http://entnemdept.ufl.edu/creatures/urban/beetles/red_flour_beetle.htm I've had issues with them a few times now, each time originating with some sort of pet food. Once it was some herby treats I got from PAH, once some grain from RR, and once some dried dandelion (!) from Zooplus. Apparently they're an extremely common pest in food storage facilities so it's not just RR. They're not harmful as such, just annoying! I've only ever had them infest one thing at a time so I've just thrown out the infested food. Never tested freezing; I'll try that next time I'm hit.
I reckon, based on my experiences so far, that what happens is food ships with flour beetle eggs hidden in amongst it, and when the weather gets warm enough the eggs hatch:
- The grain from RR was perfectly fine for months; bugs only appeared in the summer, after the weather warmed up. The grain had been in a reasonably well-sealed bag in a completely airtight tub, and the tub contained other foods which were totally unaffected, so the bugs must have been in the one bag of grain, and it's highly likely that they'd come with the bag in the first place.
- The dandelion similarly was fine for months. It came in a big bag so I left most of it downstairs in a cool cupboard, and made up a smaller bag to keep upstairs where it's a few degrees warmer. The upstairs bag erupted with bugs months later; at that time, the downstairs bag was fine. I experimentally brought the downstairs bag upstairs and soon thereafter it also erupted with bugs.
If they've gotten out into the house you'll probably see them around for a while after you deal with the source. I personally kill the ones I see, it can take a few weeks or months but eventually they stop appearing.
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