A “fire alarm” has been discovered in a plant. The Venus flytrap is renowned for its carnivorous trap that snaps shut on unsuspecting insects – when the prey touches sensitive trigger hairs an electrical signal is fired across the trap, and two signals in quick succession close the trap in a fraction of a second.
But heat-sensitive cells have also been found in the trigger hairs, acting as a fire alarm. The flytrap grows in grassy swamps in North Carolina in the US, where the grass often dries up and can be set alight by lightning, threatening the plant with serious burns.
A study simulating a grass fire made all the traps shut, but surprisingly some survived undamaged and later reopened; using a hot-air blower had the same effect. When traps were treated with a fine heat probe it triggered an electric signal at over 37C, but only over 55C was a second electric signal fired off and signalled the trap to close. The temperature also had to rise rapidly, just like a rapid fire in the wild, and so the flytrap can sense an approaching blaze and protect itself from injury by closing up.