Numerous Virds form the basis of Thanatos' army. Nobody bothers to keep count of this cannon fodder. Reapers send countless numbers of Virds on the swords of Aelion. They know that however big are losses, the Virds will recover in no time. They are excellent for devastating a peaceful settlement and distract the enemy, but their constant misconduct and low intelligence won't allow them to take part in complex preplanned operations.
Virds are closer to animals than to sapient beings like people or Reapers. By the time Thanatos descended to their planet, their civilization was lingering in the stone age. They knew keeping on fire, but they didn't know how to smelt metal or use the wheel. Their religion was really primitive: no Immortals were born in Virds' families, therefore, they had no gods.
Thanatos gave them everything: civilization, weapons, the new reason for living, which was faith and service.