The ability of the Venus fly trap to capture insects is due to:

When a fly sits on the leaf of venus fly trap, there are touch-sensitive hairs that trigger an electrical potential. This potential cause several changes which result in the movement of ions inside the cells of the leaf. Inflow of water in the cells follows which results in their becoming turgid. This causes the shutting of the trap. Related Theory The Venus fly trap is a carnivorous flowering plant. The trap is made of two hinged lobes at the end of each leaf. On the inner surfaces of the lobes are hair-like projections called trichomes that cause the lobes to snap shut when prey comes in contact with them (thigmonastic movement).