Just in case you're interested,your wee beastie is a damselfly or dragonfly nymph, not something that appears in tanks too often! It's a good job you have no shrimp yet as s/he will eat them, particularly cherry shrimp babies. If you have an outdoor pond you could put it in there or I suppose you could always leave it but as you have nothing for it to eat it will probably die...
Just a heads up might want soak the wood now, i soaked my 2 large bits for 32 days while in fishless cycle, once in the tank the water went brown for a further 7 water changes before remaining clear, wont hurt the fish but not pretty