Venus flytraps have a pretty good short-term memory for a plant. An insect has to tickle its sensory hairs twice within around 30 seconds for the carnivorous plants to close its leaves around the bug. To understand how Venus flytraps, which sadly lack brains, can "remember" when the bug first tickled them, scientists genetically engineered them to glow green in the presence of calcium, suspected to be the primary chemical agent involved in the process. From Science News:
When the team tapped one of the trap's sensory hairs, the base of that hair began glowing, and then the glow spread through the leaf before beginning to fade. When the researchers touched the hair a second time — or touched a different hair on the leaf — within about 30 seconds, the trap's leaves lit up even brighter than before, and the plant quickly snapped shut.
The results show that the flytrap's short-term memory is a waxing and waning of calcium within leaves' cells, the researchers say. Each time a sensory hair is triggered, it signals the release of calcium. When the calcium concentration reaches a certain level, achieved by that second, faster surge of calcium, the trap closes.
Still, the research doesn't reveal all of the plant's secrets. To sense prey, "the flytrap operates a fast electrical network" that can convert a fly or other insect's movement into small voltage changes that ripple across the plant's cells, says coauthor Rainer Hedrich, a biophysicist at the University of Würzburg in Germany. Scientists are still unsure how the calcium memory system works in tandem with that electrical network to activate the plant's snap.