(Those of you who follow me on Twitter know where this is going. The rest of you are just stuck reading out of morbid curiosity. Don't worry. The end is pretty morbid, too.)
So. Carnivorous plants. In general, plants turn to taking heads (haha) due to crappy soil. Nearly all (I'd say all, but this isn't my speciality in botany) of these plants grow in swamps, where the soil is notoriously acidic and nasty, and, well, a plant's got to do what a plant's got to do (incidentally, the critters are digested for extra nitrogen). There are probably more of them than you think, and they're classified both taxonomically, and by how they catch, uh, prey.
Here are the general categories.
"Pitfall traps", most of which are pitcher plants.
The 'pitcher' is a modified leaf that holds a puddle of goo that can digest proteins. All the plant does is sit there and wait for some critter dumb enough to fall in. I know these from my childhood of running wild around NE Ohio, where they were found near little streams and around standing water. If I'd know how rare they were, I'd have probably tried to stop my friends from picking them and throwing the goo on each other. But I didn't know, and we did. In the bottom of the pitcher was a pile of un-digested bug bits (the chitin exoskeleton), so it was a pretty grody thing to get thrown on you.
"Lobster pot" traps, which are related to pitcher plants. They've got very small openings in the plant, lined with hairs that look like this:
The hairs point back down into the pit of the plant, and so any critter wandering through gets stuck inside and never gets out. (Ominous music here.) These plants only trap microscopic critters though, paramecium (parameciii?) being a favorite food. So they're interesting but there's no gross-out factor because you can't see the bodies without a microscope, and what's the fun in that?
"Flypaper" traps, mostly sundews, which act just like flypaper.
The plant produces modified hairs that ooze sticky digestive juice. Flies and the like land on them and are never heard from again. Some sundews have the modified hairs on a stem-like structure, like in the photo above, and some are more like leaves. Both curl up once a victim is snared; those hairs are triggers, too.
"Snap" traps come in two types, waterwheels and the famous Venus flytrap:
These are much the same as the sundews, but with a more dramatic WHOMP sort of thing going on. Just like the sundews, there are trigger hairs inside the leaves of snap trap plants, and when the hairs are touched, the leaves slam shut. Venus flytraps are like books slamming shut; waterwheels are like an umbrella slamming closed, with the stem as the shaft of the umbrella. Incidentally, the idea in most people's heads of Venus flytraps aren't too accurate: most flytraps are incredibly small. The one I saw up close and personal, the day I heard a lecture on carnivorous plants, was at most two inches high (probably closer to one) and the 'snap' leaves were slightly smaller than a pencil eraser. One had trapped a gnat and was shut, and the gnat was a full meal for that leaf. It was in a two-inch pot (very small) and passed around hand-to-hand during the lecture.
This brings us to the most fun to watch, the bladderworts.
These little guys are often aquatic plants (though some species aren't). They just float around in the water, not doing much of anything, until some unsuspecting critter touches one of those trigger hairs. Then the bladder opens up and sucks the insect inside. Yum, yum. Eat up.
So what brought this on? A new carnivorous plant was discovered in the Philippines, and it is BIG ENOUGH TO EAT RATS. I was hoping for something really cool and dramatic like a hunormous bladderwort or flytrap (even though I knew that was physically impossible). Instead it turns out to be what I expected; a really big pitcher plant. Details here.
I love botany.