The only species other than the Venus flytrap to actively trap its meal is the waterwheel (Aldrovanda vesiculosa). This European aquatic plant floats free on the water, rootless, consuming small crustaceans, insect larvae and snails. Its snapping behavior was first observed in 1861, but the plant’s carnivorous nature wasn’t proven until Charles Darwin studied the waterwheel more than a decade later.
Aldrovanda is a free-floating and rootless aquatic plant. This plant is closely related to the Venus flytrap Dionaea muscipula, and shares many of its attributes–it functions as a snap-trap carnivore, just under water! A common name for it is the waterwheel plant because a single whorl of leaves, cut from a stem, is wheel-like, as you can see to the right! The genus name commemorates the Italian naturalist Ulisse Aldrovandi (1522-1605). In fact, the name for the genus was originally “Aldrovandia“, but Linnaeus misspelled this, and we use the incorrect spelling even today.
Each leaf in a whorl terminates in a little clam-like trap. Exactly how the trap captures prey is a little complicated. Just like the traps of a Venus flytrap, the trap lobes of Aldrovanda contain trigger hairs. When stimulated, these cause the traps to close. SNAP! The closure takes about 1/4 to 1/2 second, which is impressive when you reflect upon the fact that the trap lobes must push water as they close. If no prey is captured, the trap reopens in ten to twenty hours.