This unit is the supply source and also detector of the Zerg Swarm.This unit can become dropship after evolving Ventral Sacs ability.This evolution changes the profile of the Swarm because all overlords become dropships and which means there is a great chance to destroy the enemy by dropping.The overlords must be protected from fast corsairs ,wraiths or mutalisks.Because if they killed by these units the nightmare will begin because of insufficient limits.So be sure at protecting the overlords by any enemy assault.