Worms have simple, yet amazing biology

"How can worms break in half and live?" asked Abby Russell, 9, a rising fourth-grader at W.C. Petty Elementary School in Antioch.

Earthworms can survive rips, tears and breaks, but there are limitations, according to Doug Taron, curator of biology at the Peggy Notebaert Nature Museum in Chicago.

Worms have about 150 different segments. "You can cut a certain number of segments off at the head or tail end, but not both a the same time," Taron said.

All those segments contain different needed body parts. An earthworm has five hearts and lots and lots of intestines. The major organs are located in the worm's head and tail.

What worms don't have are eyes or brains. Instead of eyes they have photoreceptors; in place of brains they have nerve centers called ganglia. Each worm is both male and female.

Worms play a very important role in the outdoor world. They dig through soil, mixing and churning and loosening as they go. Scientists estimate that each acre of soil contains about 190,000 worms and the critters loosen about 6 inches of soil each year.

Without arms and legs, worms use tiny bristles on their segments to burrow in soil. As they move, they break up soil. This necessary process permits sun, rain and air to sink into the ground and reach plant roots, conditioning soil and providing nutrients. They chomp as they burrow, eating decaying plant life. The waste product is ready food for growing plants.

Even though they look pretty similar, not all earthworms are alike. There are more than 2,000 species of the segmented creatures. They've been on Earth for a long time, having evolved at about the same time as dinosaurs.

Get a close-up look at a worm's life by constructing your own worm bin. Directions can be found on the Field Museum's "Underground Adventure" Web site at www.fieldmuseum.org/undergroundadventure; click "Just for Teachers" and scroll to find "worm bins."