In the third edition version of the Manual of the Planes, formians are implicitly described as being the primary inhabitants of both Arcadia and the Lawful Neutral Outer Plane of Mechanus, which is in contrast to the earlier Advanced Dungeons & Dragons Second Edition, where the Modrons were the exemplar Lawful Neutral race and the primary inhabitants of Mechanus.
formian |
Once there, the characters encounter formian settlers from Mechanus, whose hive can serve as a base of operations while preparing an assault on the Iron Fortress.