Swamolas are found exclusively in the Swamp of Evil in the Dark World. Their dark green bodies camouflage them well in the swamp, and they have pronounced mandibles. They deal very significant damage to Link if they hit him, perhaps because of said mandibles. Swamolas hide under the water and muck of the swamp, lunging out to attack. They are immune to most of Link's weapons and even require many hits from the sword to defeat. However, they do not actively attack and usually are not dangerous to Link unless they surface near him.
Swamolas are related to Lanmolas. Their name is a portmanteau of "swamp" and "Lanmola". Interestingly, they are called Moldorms in the Japanese version of the game, while Moldorms are called Degu Tails.