A Sting Raid, otherwise known as Viros in the manga, is an imitation Edel Raid, possessing lesser powers than that of true Edel Raids (3 Edel Raids can finish off entire armies of sting raids). They are actually created with imitation Elemental Gelades or elemental stones. They are generally treated as tools by the Chaos Choir. Sting Raids are also different from Edel Raids in that they don't need a Pledger to React with, they can transform a part of their body.
Despite being humans implanted with imitation Elemental Gelades, there is one single instance (Viro) In which a Sting Raid can turn into a genuine Edel Raid. However, as the only known instance of this happened immediately prior to death, not much is known about if this is possible in other circumstances.