40d:Trap

(For traps used to catch vermin, see animal trap).

Traps are a reliable and cost-effective method for defending any fortress. Unlike soldiers, they're always on duty, and don't need to be carefully managed. On the other hand, they are immobile and can only lie in wait for foes to walk over them. To build a trap, go to the build->Traps/Levers menu. You'll generally need one mechanism, and at least one other component depending on the type of trap. They can be built indoors or outdoors, and require a level ground square with no other constructions in them. Most traps (exception: spike trap) are not triggered by dwarves (except berserk/insane ones), pets, caravan members and kobold thieves. These creatures will pass over traps without triggering them.

Stone-fall Trap

The simplest trap to construct, a stone-fall trap is essentially a stone suspended up in the air which is dropped on intruders when the trap is triggered. These are a popular defensive measure early on, as the components needed are readily available as soon as you start mining. A single stone trap will kill or severely maim most humanoid enemies although trolls, magmamen and hardier creatures may take two or three to drop. Mythical creatures such as dragons, hydras and titans will take upwards of five or six. After being used they need to be reloaded with another stone by any dwarf with mechanic skill enabled, a task which your dwarves will see to automatically.

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Components used: mechanism and an ordinary stone

Weapon Trap

Weapon traps consist of any number of deadly instruments rigged to a mechanism. When an intruder sets off the trap, the weapons spring out and strike the poor sap. You can add up to 10 weapons to a weapon trap, and they will all attack together when set off. This gives the potential for dealing significant amounts of damage at once. There are also special giant weapon parts you can build that are specially designed for use in weapon traps. Unlike stone-fall traps, weapon traps automatically reset after being triggered, ready to splatter the intruder's friends. But there is a (20%?)chance that the trap will become jammed each time it is triggered. A nearby dwarf will automatically clean a jammed trap; this does not require the cleaning labor. If there are weapons that require ammunition in the trap, they will also have to be reloaded occasionally. Weapon traps using bows or crossbows will not require cleaning but do use ammo.

Weapon traps are a nice way of getting rid of any cheap, mediocre captured weapons, wooden weapons you don't need for sparring and weapons your dwarves cant use. Due to the bundling of weapons you don't have to worry much about the minor damage they would cause separate.

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Components used: mechanism and whatever weapons you want.

Cage Trap

Cage traps capture creatures that set them off in cages. After a creature is captured, it's stored, cage and all, in an animal stockpile. Then the trap is reloaded with another cage. You can do all sorts of fun things with captured creatures. Creatures in cages will not be fed, they will survive indefinitely without nourishment. It is possible that dwarves bring water to cages, but that means that you have someone friendly also locked in the cage - like a dwarf kid snatched by a goblin babysnatcher. In this case remove the poor fellow using the goblin's inventory screen. A Cage trap is one of the most effective ways to defeat powerful beasts, as even a glass cage (aquarium/terrarium) can imprison a Bronze Colossus. This is expected to be changed.

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Components used: mechanism and a cage.

NOTE: This trap will not catch vermin. For that, you need an animal trap.

Upright Spear/Spike

These traps can only be utilized by attaching them to levers or pressure plates, which when triggered will cause the spikes to extend from the ground and, when triggered again, to retract back into the ground. They don't slow or hurt any creature walking through them if they are not currently triggered by a lever/plate, neither when up nor when retracted.

The lever task can be set to repeat which makes the spikes go up and down, but there is a high chance a creature will pass the spike trap before or after they shoot up, so you may want to build a row of at least 5 traps.

The damage done depends, like with weapon traps, on the number and quality of the spears and spikes used. The fact that they do piercing damage makes them useful against more powerful foes which are most easily killed by damaging their organs.

Spikes will, when triggered, damage creatures unaffected by other traps (kobold thieves and demons, but also dwarves and allied creatures). The traps' friendly fire means they make effective anti-immigrant traps. There are also reports that the spikes are effective against demons, although spikes which are not made of steel may melt.

Contrary to what one might think, the spikes appear to do no (additional) damage if a creature falls on them - there is therefore no advantage to putting the spikes at the bottom of a pit trap and you still have to connect them to a lever or pressure plate to cause injury.

Stuff does get stuck in spikes when they are triggered - any corpses will appear as an item inside a spike's 'building' when they are out (the same way mugs and whatnot appear inside workshops when you first make them). Retracting the spikes lets the corpse out.

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Components used: spears or spikes.

Other Traps

You can create even more elaborate traps with imaginative use of pits, pressure plates, levers, grates, supports, water, magma, and whatever else you can think of. Watching those goblins try to find a way out of your drowning chamber as it begins to fill is really quite satisfying.

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