With the addition of tidepools, I feel it's time to revisit the idea of other natural "containers" and ask again that they generate critters for hearthlings to discover. I quite enjoy picking through the fish to see if anything tasty shows up and It was a nice treat in salem to check stumps and occasionally find creepy crawlies to pick up and shove in your brain/butt.
For mirkwood stumps/logs, grubs would make sense. They're a useful early game food, but basically unused due to their spawn rarity. If we're concerned with game balance we could keep the spawns at Q10, who cares if someone wants to make a mirkwood farm for grubs it won't break game balancing. Other beetles and critters would also make sense, so long as we're not concerned with them causing balance issues (no ants for example) due to mirkwoods being something we can intentionally create en mass. For crevices, I think finding centipedes certainly makes sense. Why not rats and a new wound for sticking your hand in a crevice and getting nipped when you find a rat? Plenty of options for masochism! If we wanted to take it further, unique forageables that only show up inside crevices/mirkwoods would be pretty darn nifty as well.
Overall, I feel like these minor changes would help flesh the world out (frankly something haven has pushed for very successfully since full time devving started) at relatively little dev cost. I also feel most of us have always sort of expected these things to exist, and have been disappointed a little when they haven't been added yet.