Creatures with the BUILDINGDESTROYER token will actively seek out various furnishings, workshops and other buildings and topple or destroy them. They come in two varieties, the first being annoying, and the second dangerous. Buildings made from raw materials will be toppled, leaving the materials on the ground, while buildings made from furniture will be destroyed, not leaving behind any items.
Creatures with this tag are gifted with an incredible ability to sense exactly where your buildings are, and will generally charge a building from 10 tiles away, with the exception of forgotten beasts and (semi-)megabeasts. Plan your defenses accordingly. Building destroyers still prefer to attack creatures, and if a valid creature target for their aggression is or becomes visible to them, they will abandon building destruction in favor of classic creature destruction.
The time it takes for a building destroyer to destroy a building depends on the quality of the the building. Artifact quality furniture can never be damaged or destroyed, but some kinds of artifact furniture will be deconstructed by a building destroyer, given enough time: for instance, artifact statues will eventually be deconstructed; artifact hatch covers never will.
Building destroyers will destroy nearly all types of buildings they can reach, whether or not they block their path - doors, floodgates, hatch covers, vertical/horizontal bars, floor/wall grates, statues, workshops, and even furniture are vulnerable. The only buildings that will be spared by a building destroyer are wells, bridges, roads, traps (including levers and track stops), animal traps, chains, cages, stockpiles, and upright weapons. They can destroy most furniture and buildings from a lower z-level when a valid path exists to that furniture, though locked hatches and closed grates are safe as long as no alternative paths exist. They can only destroy things orthogonally. Building destroyers will path to and destroy even opened (or stuck open) doors, hatches, floodgates, or vertical bars. They will cause damage to any attached mechanisms during building destruction, sometimes leading to the unlinking of furniture to a lever before the furniture in question is fully destroyed.
 Destroying from underneath
Building destroyers cannot destroy buildings unless they can path to the building on the building's z-level. This means that building destroyers cannot destroy, for instance, a forbidden hatch above them (note that non-forbidden, i.e. passable, hatches are vulnerable!), or a magma forge from the magma underneath it unless a clear alternate path to the building exists.
Building destroyers can destroy buildings from the z-level below while standing on a ramp or stairs that leads up to the building's z-level.
Building destroyers cannot destroy closed floodgates or locked doors from a ramp leading up to the level of those buildings unless there is an open path to the same level. This was tested with trolls, in an entrance-way accessed by both lever-controlled floodgates and a manually locked door. Ramps led up to the floodgates and the door. When both were closed, the trolls showed no interest. When the door was unlocked, a troll began to destroy it. When the door was locked again, the troll went away. When the floodgates were opened, a troll returned and destroyed the locked door from the ramp outside, while the open floodgates were also apparently being destroyed from the ramps by other trolls. This may be related to the bug where Dwarves appear to be building diagonally as long as they can access the spot orthogonally. It is unknown whether this applies to an open path extending through the full length of a fortress, rather than just a few steps away through open floodgates.
Consider the following diagrams, as viewed from the side:
Building destroyer cannot pass through the cyan door while it is forbidden, but the instant the door becomes unforbidden, the building destroyer will destroy the door-- from the tile on which it stands.
Here, the cyan hatch cannot be destroyed while it is forbidden, but when it is unforbidden, the
Building destroyer will destroy it.
Building destroyer will stand on the ramp and destroy the door (or any other furniture), regardless of whether the door is forbidden.
Building destroyer will be unable to pass the door if it's forbidden; should it become unforbidden, the building destroyer will ignore the door (probably passing through in order to target a different piece of furniture).
Building destroyer has path to a square from which it can destroy the cyan door-- thus, it can destroy the door, even if forbidden, from the tile directly in front of it.
 Annoying Variety
When the value is 1, the creature will go after statues, windows (glass or gem), archery targets, slabs, wooden doors, and wooden hatches. They can't destroy homes during world gen as (semi)megabeasts.
 Dangerous Variety
When the value is 2 the creature will actively seek out buildings and destroy them. They can also destroy buildings during world-gen with this tag. Megabeasts rely on this token for their pathing when attacking your fort. Constructions (walls, staircase, floors, etc.) are still safe, since they're processed the same way natural terrain is for most situations.
The simplest way to keep building destroyer 2's from targets is with walls or channels. The outside of a raised drawbridge will act like a constructed wall, blocking building destroyer 2's without that danger of being destroyed.
Tame animals still carry their building destroyer tokens, and have been observed to occasionally topple a statue.
- Amethyst man
- Blind cave ogre
- Bronze colossus
- Cave dragon
- Fire man
- Gabbro man
- Iron man
- Magma man
- Mud man
- Voracious cave crawler
- All forgotten beasts, titans, and demons
- Werebeasts (in werebeast form only)
See the Modding guide for more information on creature tokens.
Considering a good part of the building destroyers are useful to capture, and that most of them are not trapavoid, you can easily trap them with the right arrangement of cage traps, furniture and walls.
See Trap design for more information on this subject.
- Building destroyers can, and will, destroy buildings even if there's one tile of empty space between them and the building. Bug:4585 In fact, they cannot destroy immediately adjacent buildings, and they can become stuck if they start destroying the building while adjacent. This can be a result of a fight, for instance when a Forgotten Beast kills the last defender while standing in such a spot, then it won't move to a better suiting position and will stand idling, unless killed or distracted.