One of my favorite plays is Little Shop of Horrors. It’s about a flower shop that inadvertently acquires a plant that murders people. It’s the perfect Halloween movie. Our kids were involved in their high school production; I can still see Audrey II licking her bloody lips!
Are there really plants like Audrey that need blood to survive? Well, perhaps not blood, exactly, but there are plenty of carnivorous plant species—and who knows what they do when we’re not looking?
According to the International Carnivorous Plant Society, to be classified as a Carnivorous plant, the species must:
- Capture and kill prey
- Have a mechanism to facilitate digestion of the prey
- Derive a significant benefit from nutrients assimilated from the prey
The “prey” are usually insects, spiders, and other small arthropods, but some plants don’t mind a tasty frog or lizard, or even a small mammal. These victims are an excellent source of nitrogen, which is often lacking in the sorts of places these plants grow.
A number of other plants trap insects, usually to ensure pollination, but they aren’t considered carnivorous. For example, a Lady Slipper Orchid welcomes bees into its flowers, but it’s a one-way street, due to a “lid” of petals that snaps shut behind the insects. The flower’s exit is surrounded by sticky pollen threads. The bees emerge covered with pollen, which they then carry to the next Lady Slipper blossom. Truly carnivorous plants gain no benefit from killing and eating their pollinators, so the deadly part of the plant has nothing to do with its flowers.
The Venus Fly Trap is the best known of the plants that turn the tables on their insect pests. Native to the Carolinas, they live in nutrient-poor peat bogs where they rely on insects they catch to supplement their diet. An insect lured into the folded leaves by the sweet scent of nectar may accidentally wander across two or more hair-like triggers, located on the crease in the center where the two leaves join. The trap doesn’t exactly spring shut, but it’s plenty fast enough to nab its unsuspecting prey. The comb-like teeth on the leaf edges keeps anything from escaping, and the plant slowly digests and absorbs its victim.
This process is pretty hard on the fly trap’s leaves. In fact, they wear out after only three meals, turning black and dying. And if the bug escapes (or the plant has been fooled by your finger)? The leaves can shut and open again a mere seven times before expiring. So, if you have a pet fly trap, don’t touch the leaves!
Monkey Cups, in the genus Nepenthes, develop modified leaves that develop into “pitchers” full of liquid. Instead of offering a pleasant floral scent, these tropical vines bait their traps with the smell of decay. When an unwary insect comes to investigate, it eventually realizes it’s trapped. The walls of this well are covered with flaky wax, making it impossible for the prey to climb out and escape. When it falls into the water, its struggles tell the plant’s digestive glands to secrete an acid so strong, it is able to dissolve mice!
Amazingly, there are animals that live in the pitcher plant. Some insect larvae feed on the prey as it decays. Others feed on the larvae. Ants grab pieces of the dissolving prey, then sit on the rim of the pitcher to dismember it. Some of the crumbs fall back into the pitcher where they dissolve more quickly because they’re smaller. Thus the pitcher enjoys a speedier meal.
Other carnivorous plants catch their dinners in other ways. According to the Botanical Society of America,
Flypaper (or sticky or adhesive traps) of sundews and butterworts are leaves covered in stalked glands that exude sticky mucilage.
Suction traps, unique to bladderworts, are highly modified leaves in the shape of a bladder with a hinged door lined with trigger hairs.
Lobster-pot traps of corkscrew plants are twisted tubular channels lined with hairs and glands.
The next time you go out to eat, keep an eye on that decorative tropical foliage behind you. That plant with the large leaves might be related to Audrey!