Vault Skirges are Phyrexianized skirges.
Vault Skirges are created by Geth and his cohorts to bring back vital flesh and fluids to Ish Sah for use in creating his Phyrexian monstrosities. They fly in and attach themselves to their prey with a powerful claw, they then either bite a chunk of flesh off or suck a victim's blood before flying off to their master, delivering their stolen payload.
From the remnants of the dead, Geth forged a swarm to safeguard his throne.
