Learning from Nature: the Mechanics of Traps

A fascinating article in the Atlantic describes the mechanism of the Venus flytrap as scientists have studied it. It's a great description of the Venus flytrap's mechanics, which through evolution shows how an unthinking plant can hijack the instinctive survival response of an animal. Its process is instructive in how we can think about trap design.

First, the trap is appealing. A fly comes along because it smells something sweet. By making itself attractive the flytrap uses the appearance of other plants around it as an offensive weapon. Since the fly can't tell immediately that it's a trap, it comes in to inspect. Only then is it doomed. This is a good principle for elaborate traps in D&D. PCs are always looking for treasure. Appearing to present a treasure is a good way to present a trap, but not the ideal way.

D&D players aren't, no matter what some referees may tell you, as dumb as flies. A trap that's simply too obvious, such as a chest of shimmering jewels and gold coins unguarded in the middle of a room, will be regarded with the utmost paranoia. It's obviously a trap. A really great baited trap is one that looks like hidden treasure. It's hidden in a secret compartment or panel that can be found by careful PCs. Such a subversion is cruel, but sometimes the best way to spring a trap on players is to make them work for it.

Second, the trap has error-checking. It only closes when two of its cilia are brushed. This is a wonderful principle for mechanical traps: the trap is not triggered on the first pass. The primary reason for this is to avoid false alarms, as described in the article. This is good and pragmatic. But with a D&D style trap, there is a further benefit where the party is drawn deeper into the trap before it springs. A simple pit or arrow trap will kill only one member of a party, but it is reasonable for trap designer to aim for multiple kills. And it may also be a way for monsters (or clever PCs) to avoid a trap by letting it reset after the first trigger.

There are two good ways to implement this principle with a D&D trap. One is to require a single trigger to be pressed more than once, such as a pressure plate that activates a two-step process. The first step cocks the arrow and the second fires it. The other is to have two separate triggers, one that starts the trap process and a second that finishes it. Either can work and both are nasty surprises.

Third, the trap imprisons without killing. This can be useful in a faction dungeon where the monsters might prefer to question a member of a rival group spying on their territory rather than killing them. The victims of such a trap become useful bait or can be traded in a prisoner exchange. This can lead to a tense period where the PCs have an opportunity to try to escape before the monsters who set the trap come to check it. Or the designer may have abandoned it and the trapped characters are stuck until a wandering monster comes along.

A trap that doesn't kill outright is extra fun if it affects only a single PC. The rest of the group simply sees the lead PC go missing and isn't sure exactly where they are, while the trapped character has to deal with their predicament on their own. It presents the immediate dilemma of how much effort to spend on saving the trapped character. And as noted about the factions above, such a PC may be a bargaining chip that stops the rest of the characters from barging in and killing a monster group.

Fourth and most brutal, the trap makes its victim kill itself. The fly's struggles against its captivity doom it. Standing still would be the best policy, but it goes against their instincts. This can be copied in straightforward ways, such as by having the character trapped so tight that they can't struggle to get out without impaling themselves on a spike, or puncturing a container of poison gas or acid. It could also be a question of physics, if the trap is suspended more than 10' above the ground. Even a simple quicksand type of trap, where struggling to extract yourself actually pulls you in further, does a great job with this principle.

But this can be used in more devious and subtle ways. Efforts to escape can let the players, who again are still smarter than flies, outthink themselves. Elements of the trap itself may be unstable or unsafe, or designed in a misleading way. What looks like it will open a door actually operates a hidden ballista, or opens a chamber above full of heavy rocks. You can go way too far in this direction and wind up in Grimtooth's Traps, but I think there's a lot of fun trap design short of that.

I love the concept of the Venus Flytrap. It's an elegant and simple life form, and does its work without even the simplistic thought patterns of the fly, but it does something very intricate and involved. Its principles can lend a lot to any trap in your dungeon, whether you pick one or all four.

Oh, and don't forget the simplest way to apply lessons from this article in your dungeon: giant Venus Flytraps.

Carnivorous Plants and the Dungeon

Reading about exotic South American mountains and their unique flora got me thinking about pitcher plants, which are also known as pitfall traps. These tend to be small, exotic plants that trap insects and convert them into nutrients. The pitchers of plants like Nepenthes lowii, pictured to the left, tend only to run as long as 35 centimeters (just over a foot). But this is Dungeons & Dragons; if there is one thing the game is good at, it's taking things and making them bigger.

You probably already know where I'm going with this. Sticking a pitcher plant, particularly one with a snap-shut "lid" like Nepenthes lowii, in a D&D pit trap is a wonderfully nasty surprise. The hapless dungeon delver falls in, and all of a sudden they're trapped in a suffocating plant, trying to get some weapon free and cut their way out while they still have air left. Meanwhile the digestive liquid burns them as it starts to turn them into plant food. Their friends can to try and cut them out, but that's pretty dangerous.

The tentacle of the sundew Drosera capensis is another nasty trap. When the long hairs are sprung, the sticky tentacle curls up and rolls its prey into more of its digestive juices. This one might, depending on size, do crushing as well as acidic damage as it entraps a character. These liquids should, by the by, also be doing a number on armor even if the PC gets away; a coat of mail or plate that is scarred and pitted by acid is no longer useful for defense. These can be in pit traps as well, or used as room traps in a weird sort of "garden room."

It should be obvious why carnivorous plants are the kind that thrive in a dungeon, of course: lacking much in the way of sunlight, dungeon plants will consume flesh. And it lets you have plants in your underworld in a semi-logical way.

Of course, we can hardly discuss carnivorous plants without talking about the Venus flytrap. Once the trigger hairs on this plant are sprung, its powerful leaves snap shut and the unfortunate insect caught inside is done for. A huge flytrap can catch a single character, but a really massive one could even get a whole party. Again we're relying on the combination of crushing damage and acid to actually do in the character. The initial blow as the flytrap shuts might also do some damage. They're iconic and, like the pitcher plant, will pose the difficulty of freeing a trapped character without harming them. Dungeon variants might have hardened bristles that do damage while the flytrap closes.

Plants, of course, are typically something we see only above ground. This makes their appearance in the dungeon setting startling, and clearly the sign of weird Chaotic mutation and/or a mad wizard's experimentation. Of course, you could always go full-on Little Shop of Horrors or Attack of the Killer Tomatoes as the end stage of dungeon carnivorous plants; but I think the initial horror of being consumed by a pitcher plant in a pit trap or caught by a giant sundew is a great way to incorporate some plant life into your dungeon crawls.

Sundew image by Noah Elhardt CC-BY-SA
Venus flytrap image by Noah Elhardt CC-BY-SA

Cryptid Corner: Raskovnik

I've re-assigned the old Cryptid Wednesday posts to a category called "Cryptid Corner," the new name of this feature. I've left the old names of the posts but the tags are all corrected. Today we go to the Balkans for a cryptid plant rather than a creature as such.

Raskovnik

In remote and distant fields grow an herb called raskovnik, or thief's clover. It grows in close proximity with other herbs, and an untrained eye could pass over a specimen a hundred times without ever espying it. The herb can be found with some difficulty by druids, yielding at best 1 quatrefoil per hour. Tortoises and snakes are quite capable of finding it, and will be able to direct a character to a clump of 1-6 quatrefoils per hour. This never reaches more than 10 quatrefoils found in a given field in a month.

When the stem of a raskovnik plant is placed in a lock for 1 turn, the lock will be opened (it is permanently broken). This applies to all non-magical locks, regardless of complexity. Inserting a raskovnik stem into a trapped lock will trigger the trap on a roll of 1-2 in 1d6. A Wizard Locked door can only be opened by a number of raskovnik quatrefoils equal to the level of the magic-user who cast the spell. Other magical locks are similarly effected.

A tea can be brewed from at least six raskovnik plants in eight ounces of water. This must be steeped for at least 4 hours to gain the desired effect, and the plants so brewed lose their lock-opening powers. The remaining tea is strongly concentrated and, if drunk, will grant the ability to detect the largest treasure within 120' of the imbiber for 2-12 turns.

Rodents have an insatiable appetite for raskovnik. Hedgehogs, giant rats and other rodent-like creatures within 60' of a raskovnik plant (living or cut) can smell it and will seek to devour it immediately, ignoring anything that comes between itself and the plant.