Maybe hermit crabs could be spawned intentionally? Say, a sewer crab has a 10%(or maybe 25) chance of fleeing when at 50% HP or lower. When the crab finds its way next to a barrel, it takes a turn before turning into a full health hermit crab.

This change would let the player decide whether to permit the transformation, provided they have the means to take down the fleeing crab, and gain a risk-reward scenario. With the abundance of barrels, if you’re taking on a crab next to some, the fight could escalate quickly.

Each spawn rate in this way probably needs to reduce the flee rate by half to limit farming.