How does a Venus flytrap tell a real insect from a falling raindrop?

Question

AhaDaily · Accepted Answer

Its trigger hairs must be touched twice within about 20 seconds The flytrap counts: its trigger hairs need two touches in about 20 seconds before the trap closes, so one raindrop never counts. At Würzburg, Rainer Hedrich's team showed one touch of a trigger hair fires one signal, gone in about 20 seconds. Rain and sand never fool it, because only a second touch inside that window shuts the trap. Digestion starts only after the fifth signal.

How does a Venus flytrap tell a real insect from a falling raindrop?

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