A Venus flytrap typically has three trigger hairs on each lobe. These sensitive, hair-like structures sit on the inner surface of the trap and detect contact from insects or spiders.
The trap does not usually close after a single accidental touch. Two hairs must be stimulated in succession within roughly 20 seconds, or one hair must be touched twice quickly. This threshold helps the plant avoid wasting energy on raindrops, dust, or other harmless debris.
When triggered, electrical signals spread through the leaf and cause the two lobes to flip inward. The marginal teeth then interlock around the prey. The hairs are different from the stiff fringes along the edge, which help keep captured insects from escaping.
The Venus flytrap is the only species in the genus Dionaea. It evolved in nutrient-poor wetlands of North and South Carolina, where capturing small arthropods supplements—rather than replaces—ordinary photosynthesis.