Well, we cleaned out the cupboard last night. Little sods were everywhere.

I'm sure there are still a few hiding in the joints between the cupboard panels, so I'll be keeping an eagle eye out for any more of them wandering about.
I also discovered that our 'airtight containers' are nothing of the sort. Just cheapo imitation things from some tatty cookshop in Hemel Hempstead. Looks like we need a tupperware party. There's no way I'm having this again - we've been having to buy our bread from the shop until we could get everything clean and re-stock with flour.