Venus flytraps, the most famous carnivorous plants, just got a little creepier. These plants can count the number of times a hapless bug triggers one of their sensors, and they adjust their behaviour accordingly. They don't have a brain, obviously, but a series of number-dependent biochemical pathways make these flytraps the mathematical geniuses of the botanical world.

What happens when a venus flytrap counts? A flytrap will not snap shut the first time a bug touches a trigger hair. It takes a second touch-- to distinguish a bug from a raindrop-- for the plant to snap its trap closed. And as the bug* activates more triggers in its struggle to escape, the venus flytrap "counts" activations and produces a proportional amount of digestive enzymes. Three trigger activations? Not too much enzyme needed. Ten?! Get cooking, enzyme producers!

See a captivating video here (produced by the researchers) to watch these plants count: http://www.cell.com/cms/attachment/2044746873/2056484057/mmc3.mp4

Why and how do brainless plants adjust their behaviour based on counting? The why is easy: carnivory is energetically expensive, and it would be a big waste for a plant to snap shut around a raindrop! So these plants evolved a sensitive hair-trigger system (literally) that helps them differentiate between a bug and a raindrop, and even between a big bug (many triggers activated) and a small bug (fewer). Estimating prey size helps them produce the right amount of digestive enzymes.

How they can count is slightly trickier. Venus flytraps have a number of finely tuned hair triggers on their surface; when one is touched, action potentials fire. Two touches in a row activate the "closing" mechanism. Once the trap is closed, more touches of the hair triggers  (totaling 3 or more) initiate expression of genes that create digestive juices-- "prey-degrading hydrolases." The more times a bug struggles and bumps into a trigger, the more digestive juices the plant makes (which is possible through direct modification of gene expression). Further, the plants love to take up sodium from their insect prey using a sodium channel: just like the amount of digestive juice produced, the amount of transcripts of the sodium channel depend on how many triggers the struggling bug activates. In simpler terms, the more the bug struggles, the more the plant reacts-- both by preparing digestive juices and getting ready to absorb the nutrients from its prey.

Sure, these plants aren't exactly doing calculus. But the singing flytrap from Little Shop of Horrors doesn't seem quite as impossible now.

See the open-access original research paper here: http://www.cell.com/current-biology/abstract/S0960-9822(15)01501-8

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* "an animal meat" in the original paper's apocalyptic parlance