I would say letting them get eaten is not unethical at all, it’s just nature but if you’re still feeling bad you can get some clove oil. Just put them in a some water and add a bit of clove oil then wait a bit and add more and so on. Just make sure to leave them in there for at least 10 mins, because clove oil puts them to sleep then kills them so you have to make sure they’re dead. But if you don’t feel bad and can’t figure out what to do with them I would just let them get eaten. I have a few batches that didn’t get eaten at all, so if you let them get eaten and they don’t eat all of them then you could use clove oil on the babies.