The Carnivorous Plant FAQ v. 12

Q: How do carnivorous plants digest their prey?

Sarracenia flava
S. flava contents

Drosera binata
That's gotta hurt!

A: Carnivorous plants must have use enzymes to digest their prey. Most carnivorous plants, such as Venus flytraps, sundews, butterworts, and many genera of pitcher plants all make their own digestive enzymes. After their captured meals have been digested, all that remains is a sickening mass of crunchy bits that will put you off popcorn for a long time. (More because of the the texture than the flavor.)

Other carnivorous plants (such as Heliamphora) rely on bacteria to produce the appropriate enzymes. In this case, the plants themselves do not excrete the digestive juices. The food just rots, and the carnivorous plants absorb the decomposed molecules. Many plants, such as Sarracenia (and notably Sarracenia purpurea) rely upon both their own enzymes and bacterially generated enzymes. This is called a symbiotic (or mutualist) relationship, because both organisms benefit from the cooperation. The plant enjoys the bug-soup digested by the bacteria, while the bacteria get a nice place to live. Incidentally, as I have noted earlier in the FAQ, bacterial symbioses are common in the animal world--termites have bacteria in their guts that enable them to digest wood, and humans have E. coli in their guts to help them with their digestion.

A third trick that some carnivorous plants use is arthropods such as insects such as hemipterans like Pameridea or Setocoris (commonly misspelled as "Setocornis") or midge larvae (Metriocnemus sp.). A famous case involves critters called assassin bugs that live on carnivorous Byblis, Drosera and Roridula. These assassin bugs crawl around on the carnivorous plant and eat the poor insects that have been captured. It is amazing the assassin bugs do not get caught themselves. The bugs then poop, and the excrement is absorbed by the plant. Yum yum! Bug poop!

As I note elsewhere in the FAQ, some people question if the plants that rely upon bacteria or arthropods to help them perform digestion should really be called "carnivorous," and should be called something else like "paracarnivorous." I doubt there is any resolution to this tedious discussion. Nature presents us with a continuum of processes, and trying to classify the Universe into clear-cut categories is not always fruitful. Black and white distinctions only occur in the Star Wars1 movies, and not reality.

Perhaps the most horrible of all the adaptations in the world of carnivorous plants and their allies, are the lifestyles adopted by some species of Nepenthes. These may function as places where birds poop. The produce food for the birds (little globs of goo tasty to avifauna). While the birds sup, they poop. The poop slides or drains into the pitcher for consumption by the plant. Nothing like a little flavorful, gooey bird doo-doo to get you going in the morning. (If this is correct, the acronym "ICPS" for our beloved carnivorous plant society does not have to be changed. It could just stand for "International Coprophagous Plant Society"!)

1I hope this reference to Star Wars satisfies those people who complain that I only make Star Trek or Lovecraft references in the FAQ, and that I do not make suitable obeisances to Yoda (who Spock could whup any day of the week) or young Mr. Skywalker (Luke vs. Kirk?...not too hard to figure out the winner in that one either! One Federation karate chop and it would be all over for li'l Jedi boy!).

Page citations: Clarke, C. 1997, 2001; Frazier, C. 2000; Gallie, D.R. & Chang, S.C. 1997; Hartmeyer, S. 1997, 1998; Juniper, B.E. et al. 1989; Rice, B.A. 2006a.

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Revised: 2018
©Barry Rice, 2018