The mutalisk has been little changed from its original form, the roving mantis screamer of the desolate Dinares sector. In their original forms these creatures were capable of atmospheric and deep-space flight, although how they accomplished such a feat is poorly understood. Apparently they were even capable of migrating between stars, presumably while in some kind of larval form.
Proof of this amazing interstellar capability can be observed from the towering aeries of the mantis screamers that are a common sight on lifeless worlds across several star systems. Most such nests are empty and abandoned now that this highly successful and adaptable species has been infested by the zerg and evolved into mutalisks.
Mutalisks form the primary flying forces of the zerg, making hit-and-run attacks against vulnerable installations and wheeling across the skies in prodigious numbers above zerg nests or land-based forces. Many attempted engagements with the zerg have collapsed due to the rapid arrival of large numbers of mutalisks before any meaningful air defense could be mustered. Under these circumstances the total loss of the forces involved is virtually guaranteed.
Conversely powerful air defenses have succeeded in keeping mutalisks at a distance, for the creatures are limited in vitality. However, they remain agile and dangerous opponents. A mutalisk can attack foes both in the air and on the ground by expelling a glaive wurm: a voracious symbiote that can rapidly strike at several opponents as it explosively disintegrates. In large numbers or against weak defenses, mutalisks will always be a deadly threat.