Hullin 67: More Creepy-Crawlies -- and the Leviathan

Rav Huna says not to pour beer in the night with a filter, lest a creepy crawlie comes outside of the filter and into the beer, which would be a problem to drink. How does one distinguish between that which is just the normal manner of growth, which would be acceptable, and when there's a problem of unusual bug activity. Also, an investigation into the question of worms - in that they come from outside of the animal, as compared to internal "spontaneous generation." What about larvae? And what about fish larvae? Also, again, "according to its kind" - for a worm and a scorpion and a beetle and a centipede. That is, those creepy crawlies that are not considered kosher. Plus, the Leviathan, which doesn't reproduce, is a kosher fish -- and it will be the feast for the righteous in the future.