Read the Formian entry in the MM, it specifically states that they are capable of very impressive and harmonious battle plans and maneuvers through use of the Hivemind and being directed by the more powerfull and intelligent broods.
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And PC, you might wanna hit their Instant Fortress with this if you really want to annoy them ^^
Quagmire Vortex
Evocation [Earth, Water]
Level: Drd 9
Components: V, S, DF
Casting Time: 1 standard action
Range: Long (400 ft. + 40 ft./level)
Area: 80-ft.-radius spread
Duration: 1 round/level (D)
Saving Throw: See text
Spell Resistance: No
This devastating spell can be cast only in swampy or muddy environments; the entirety of the spell's spread must be located in this terrain or the spell fails.
When cast, the bog in this area lurches into a sluicing life, forming a vortex made of mud and peat not unlike a huge whirlpool. The violent churning motion of the vortex knocks down creatures, collapses structures, and inexorably pulls anything caught in its area toward its center.
Each creature standing in the area must make a Reflex save (DC 15) each round they remain in the area or fall down. Structures in the area take 50 points of damage per round. Any creature caught inside a structure that collapses takes 8d6 points of bludgeoning damage (Reflex DC 15 half) and is pinned beneath the rubble. A creature pinned beneath rubble takes 1d6 points of nonlethal damage per minute while pinned. If a pinned creature falls unconscious, he or she must make a Constitution check (DC 15) or take 1d6 points of lethal damage each minute thereafter until freed or dead. Unfortunately, pinned creatures may be in for an even more terrible fate as they are drawn toward the center of the vortex.
Each round, all creatures that have fallen down and all structures that have collapsed move in the same circular pattern around the center of the vortex at a speed of 30. Each round, this motion draws objects 10 feet closer to the vortex's center.
Creatures on the ground that have not been knocked prone move in this manner as well, but this movement does not count against their maximum movement for the round, and, on their turn, such creatures can take move actions to move in any direction they wish. The thick mud reduces the base land speed of Large or smaller creatures to 5 feet, and it does not hinder creatures larger than this. If a creature has a natural swim speed, it may use this speed instead while in the mud.
Once an object or creature reaches the center of the vortex, it is pulled down into the mud at a rate of 30 feet per round to a maximum depth of 80 feet. Creatures pulled into the mud begin to drown whenever they can no longer hold their breath (see the Swim skill description in Chapter 4 of the Player's Handbook, and Drowning in Chapter 8 of the Dungeon Master's Guide). Characters held below the surface of the vortex can swim back toward the surface with a successful Swim Check (DC 35 + 1 per consecutive round of being under the surface).
Once the spell's duration ends, the vortex instantly calms. Trees and other natural vegetation are naturally returned to their positions before the vortex began, but creatures and artificial objects (including ruined structures) pulled down into the vortex become imprisoned in the mud; living creatures that do not have burrowing speeds quickly suffocate if not rescued.
Balanced well, of course, in that any high-level character with a means to fly or otherwise transport itself isn't in any danger, plus the fact that it must be cast in mud. But still - it certainly would be very impressive to witness! 
