Bladderwort: The Fastest Predator in Lake Champlain

Hidden in the shallows of Lake Champlain lurks a predator who engulfs its unlucky prey in milliseconds, waiting for its next meal. This speedy carnivore is neither freshwater shark nor sinister cryptid cousin to Champ, but rather a harmless-looking native plant: the Common bladderwort.

Bladderworts (Utricularia) are distributed worldwide—there are 285 species of Utricularia, making it the largest genus of carnivorous plants on earth. While plants are commonly viewed as peaceful photosynthesizers, those considered carnivores have adaptive traits that enable them to capture and kill prey in specialized traps, digest the prey and absorb its nutrients, then use these nutrients for plant growth. Carnivory evolved in plants independently at least a dozen times, so bladderworts are not necessarily closely related to better-known meat-loving flora like the Venus flytrap. 

Common Bladderwort (Utricularia vulgaris spp. macrorhiza) is found in all 50 U.S. states and makes its home in Lake Champlain. Bladderwort is a free-floating submersed aquatic plant, which means that the plant lives almost entirely underwater and does not root into sediment. It appears non-descript: each plant consists of a stem that grows about eight inches long covered in slender, alternating leaves roughly one inch in length. 

How does such a simple looking plant eat? Unlike the two large leaves that form a “mouth” for the Venus flytrap, the delicate bladderwort leaves are interspersed with tiny dots. Upon inspection, these speckles are small bladders—the word “utricularia,” from which the scientific name is derived, is Latin for “little bag.” These structures are traps for their prey. 

The bladder trap, when "set," is under negative pressure in relation to its environment. The trap opens when hapless prey bump against the microscopic hairs around the bladder. This mechanically triggers the bladder to open, pulling in water and whatever is floating in it. Bladderwort will eat just about anything that fits in their traps: water fleas, nematodes, bits of algae, small crustaceans, and even mosquito larvae.

Once the bladder is full, the trap seals. The whole process from trigger to re-sealing the bladder takes about 10 milliseconds—100 times faster than a Venus flytrap—and water is sucked in at a remarkable force of 600 g (or six hundred times the force of gravity). According to the Guinness Book of World Records, this makes bladderwort the fastest predatory plant in the world. Once the trap seals, the plant releases digestive enzymes into the bladder. Captured prey dissolves over the course of a few hours, although some protozoa appear to be highly resistant to the enzymes and have been observed to live for several days inside the trap. 

Advances in microscopy and high-speed cameras have allowed researchers to study this surprisingly sophisticated trap system more closely. Research suggests that bladderworts form symbiotic relationships with microorganisms around their bladders, possibly to help attract prey and assist with digestion. The microbial communities observed around bladderwort traps are extremely rich, akin to the gut flora of herbivorous animals.

Bladderwort has an appealing blossom that contrasts with the small-scale gore the plant inflicts beneath the water. Yellow petals surround a flower similar in appearance to a snapdragon that pokes out from the water and usually blooms in our region in mid-July. This plant is relatively common in Lake Champlain—you can find it in calm, shallow areas with lots of plant activity such as the Sand Bar Wildlife Management Area in Colchester, Vermont and Cumberland Bay in Plattsburgh, New York. It also lives throughout the watershed in bogs, ponds, and marshes.