Predators are available as a special anti-infantry unit at the cost of 15 zerg research points and the Hercules dropship. They unleash a Lightning Field AoE burst which deals 20 damage with every attack.
While they gain no bonus against any unit type, a handful of them can easily bring down swarms of zerglings or other low health units with their AoE burst attack.
↑Furman, Simon (w), Federico Dallocchio (p, i), Milen Parvanov (col). "StarCraft #2" StarCraft1 (2) (June 24, 2009) DC Comics (Wildstorm).