The Venus flytrap is a carnivorous plant native to the subtropical wetlands of the Carolinas. It gets nutrients missing from its habitat by trapping and digesting insects. The plant’s trapping mechanism uses specialized leaves that form a clamshell-like trap equipped with sensitive trigger hairs that, when stimulated, initiate the rapid closure of the leaf lobes.
What Are Trigger Hairs?
Trigger hairs, or trichomes, are small, bristle-like projections on the inner surfaces of the plant’s trap. Each trap has two lobes, with three trigger hairs on the interior face of each. Their placement ensures an insect crawling on the surface will contact them. As mechanosensors, these hairs respond to physical touch, which begins the process of capturing a meal.
How Trigger Hairs Work
The trigger hair mechanism conserves energy and avoids false alarms from stimuli like raindrops. The trap will not shut from a single touch. For it to close, two separate stimuli must occur within about 20 to 30 seconds. This can be two touches on the same hair or one touch on two different hairs.
When a trigger hair is bent, it generates an electrical signal called an action potential. This initial signal is not strong enough to close the trap but instead primes it by releasing calcium ions. A second touch generates another action potential, raising the calcium concentration enough to initiate the trap’s closure.
This rapid change is achieved through osmosis, as a sudden shift in water pressure causes the lobes to change from a convex to a concave shape. This action snaps the trap shut in less than a second.
The Plant’s Response to a Trigger
After the trap snaps shut, the process is not complete. The lobes initially close loosely, with their interlocking cilia forming a cage that allows very small insects to escape. If no further movement is detected, the trap will slowly reopen over about 12 hours.
If a larger insect is caught, its continued struggles will repeatedly stimulate the trigger hairs. About five more touches signal the trap to seal completely. This tight seal makes the trap watertight and triggers glands on the leaf surface to secrete digestive enzymes.
The plant digests the insect’s soft tissues over 5 to 10 days, absorbing the nutrients. After digestion is complete, the trap reopens, revealing the indigestible exoskeleton. Each trap can only perform this action a few times before it withers and dies.