Each spring, yellow or white flowers brighten the surface of bogs, marshes and stagnant ponds. Are these the flowers of buttercups or water lilies? No, they belong to the bladderwort plant, a carnivorous plant that does all of its feeding below the waterline. However, most overlook this point since the visible parts of the plant suggest nothing of what happens underwater.
Each small flower produces seeds that later germinate into the next year's bladderwort plants. Most are annuals, but a few perennial varieties develop thicker roots for overwintering in mild climates.
Bladder what? Only during modern times have microscopic techniques allowed researchers to study the bladder traps that grow from roots below the water level. The name is much older, and these traps which are below the water line only show their hollow bladder shape when magnified. Some sources suggest that the common name is from these traps, but some bladderworts have traps with flattened side structures that suggest other shapes. Likewise, the flower is not bladder-shaped, but instead resembles an orchid or jewelweed. However, the plant was once brewed as tea for treating urinary tract infections, similar to cranberry. Today, it is still available and is available as supplements and tea for UTI's. The “wort” part comes from the Old English word for “plant.” It seems that the name is more likely to come from the plant's imagined health benefits.
Bladderworts are not the only creature that moves fast when catching prey. Single-celled plankton like radiolarians and freshwater vorticella develop vase-like structures that circulate water in a helical path. Likewise, plankton found in ponds and stagnant water circulate water.
Imagine the centripetal forces in vacuum cleaners that gather dust particles to the center of a cylinder. The heavier particles move towards the center of swirling air currents, to separate them before the air passes through a fiber filter. Aquatic filter-feeders have mastered this trick long before infomercials ever pitched them over late night airwaves or deal-a-day sites offered them to early morning web surfers. Within their funnel structures, plankton particles sweep to the center of a water vortex before passing into the digestive tract. Not all of the traps need an external trigger. Some some traps are metronymic, triggering about every five hours, trapping phytoplankton and bacteria that might aid digestion.
Bladderworts move fast. In less than ten milliseconds, they can spring their underwater bladders to suck in a tasty treat before it can swim away. Wandering waterfleas (daphnia) bump into one of multiple trigger hairs and get sucked inside faster than they could dart away. Inside the trap, the bladderwort digests their proteins for scarce nitrogen and minerals like phosphorous potassium calcium Unlike radiolarians and vorticella, bladderworts do not limit their diet to what will fit inside their suction trap. That is, bladderworts won't bite off more than they can chew. If a tasty tadpole or other mega-morsel ends up in a trap, they can digest it in stages, as long as the bladder trap seals out water from the outside. Nematodes, mosquito larvae or even newly hatched fish are all on the menu. After the larger prey is small enough to fit inside the trap, its door will close behind as for smaller particles.
False alarms trigger traps, which reset in a few minutes. Some studies have measured how fast traps close, how sensitive their trigger hairs are, timed how long it takes to digest fully trapped particles. However, the studies don't compare the trigger and reset times between young and old traps. Older traps might be expected to fatigue and become less effective, just like venus fly traps or the sprawling arms of sundews eventually wear out after too many cycles. Other green carnivores like pitcher plants have traps with limited lifetimes, so all of these plants continually regrow new traps as the old ones wear out.
Bladderworts are efficient and adaptable. They feed on abundant plankton even in nutrient-poor waters, and can become invasive and crowd out other species. Along with milfoil and elodea, they can clog slow-moving streams as they proliferate when individual plants form a thick mat at the water's surface. Have a terrarium or Water Garden? You wont need a green thumb to keep bladderworts happy. They're available online, and good for aquariums or small ponds.