Banelings are created from zerglings following a brief chrysalis phase. In the new form, the zergling's claws shrivel and become withered, and a swollen sac filled with volatile chemicals grows out of its back. The zergling's skin is repurposed, stretching over newly formed growths while its bone plates soften to hold bulbous, pulsating acid sacs in place. Though the remains of the carapace offer no real protection, they allow for unhindered delivery of the baneling's payload. The digestive and reproductory tracts are assimilated as nutrients to accelerate the process, and make room for the fleshy, mutated adrenal glands. These are re-purposed to produce and store large quantities of highly corrosive acid. Few materials can withstand this acid burst.

When a baneling gets close enough to an enemy, it triggers a reaction within its volatile chemical payload, causing the creature to explode with a shower of searing acid. The explosion destroys the baneling but also inflicts terrible damage to its enemies, highly effective against both structures and ground forces.

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