Thursday, October 6, 2011

Carnivorous plants--Bladderwort in Black Pond

by Rex Merrill

You don't know what lurks below the surface unless you look.

One of the joys of living near a pond is being able to get out on the water for a paddle on a sunny summer day. I often make a quick circuit in a canoe or kayak just inside the zone of submerged aquatic vegetation.

Bladderwort is found in shallow water along the shore of Black Pond, near the isthmus.

Sometimes I'm frustrated by having to paddle through thick beds of invasive European water-millfoil, but other times I slow down to take a look at the variety of life just beneath my boat. On such a paddle I ran across the bladderwort, a fascinating plant that eats aquatic invertebrates.

The bladderwort is easy to miss. Its highly branched shoots float just beneath the water surface and may be mistaken for the finely divided leaves of the water-milfoil that often grown nearby.

When bladderwort blooms, it sends a stalk 4-12 inches above the water with several purple flowers which are over half an inch wide and reminiscent of snapdragons.

Once you find the plant and pull it above the water's surface, you should see the small bladders (each about a sixteenth of an inch in diameter) that give the bladderwort its name.

Lurking under Black Pond...  The round leaves are water lilies.  The feathery leaves are bladderwort. The small, dark, beanlike structures are the bladders. Click photo to enlarge.

Bugs beware

The bladders are hair-triggered traps that catch aquatic invertebrates such as mosquito larvae and water fleas. The trap is set by pumping water out of a bladder and closing a trap door. The trap is sprung when an unwitting invertebrate trips the trigger hairs that surround the door.

When the trigger hairs are tripped, the door snaps open so that water and invertebrates are sucked into the bladder. I've actually heard the traps snap open.

Once the prey is caught, it suffers a prolonged death as it is dissolved by digestive enzymes produced by glands inside the traps.
#          #          #

Rex is a professor at the University of Wisconsin--Baraboo, and a Board Member of Friends of Lake Wingra.  This article first appeared in the newsletter for Friends of Lake Wingra. 
A few minor changes have been made to adapt the article to Cape Cod.  For example, there are several species--Rex was writing about the common bladderwort (Utricularia vulgaris), with yellow flowers.  The one in Black Pond is apparently a closely related species with purple flowers.  It was blooming on July 17, 2011.

No comments:

Post a Comment