Quakers are Zerg units created by Naghul, Lord of Vipers, that make an organic minefield. These grotesque horrors can move while burrowed, deploy Volatile Parasites, and overall make certain choke-points impassable.
Quakers were created from Crawling Blothrears, ancient slug-like beasts known for making massive hives, each hive as big as Earth's moon. Their backs were covered in large buboes filled with wax that hardened quickly after being administered. Now, they're a deadly anti-siege unit able to make almost any choke-point impassable to most units.
Their ability to move while burrowed is quite powerful, when combined with their Parasitic Discharge ability.
In their purple blood, they store millions of volatile parasitic larvae, just waiting to be called into the buboes and be made into living land mines. The buboes are technically incubation pods, filled with growth hormones that make the larvae into organic spider mines, unburrowing, charging, and detonating, in an acidic explosion, able to penetrate through most armor.
Their 6 burrowing claws, made after the Roach's scythe-like blades, allow it to burrow at incredible speeds, as well as kill enemies of the Swarm who get too close. Its acidic saliva, not as acidic as the Roach's, but still potent, allows it to literally eat through most metals.
Quakers are effective against single heavy units and large groups of light units.