Plural for bacterium, a one- celled organism which can be seen only with a microscope. Bacteria may be shaped like spheres, rods or twisted springs. Some bacteria cause decay; others may cause disease. Most bacteria are beneficial because they help recycle nutrients.

A geographic zone such as an ocean, desert, or glacier which would prevent the migration of an earthworm. Barriers may be different for other kinds of animals.

Moisture- retaining medium which provides a suitable environment for worms. Worm bedding is usually cellulose- based, such as newspaper, corrugated cartons, leaf mold, or compost.

Capable of being broken down into simpler parts by living organisms.

Management of pests within reasonable limits by encouraging natural predator/prey relationships and avoiding use of toxic chemicals.

A scientist who studies living things.

A liquid medium circulating in the bodies of many animals. Blood carries food and oxygen to the tissues and carries waste products, including carbon dioxide, away from the tissues. Earthworms and humans both have a red, hemoglobin-based blood for oxygen transport.

To carry on activities to permit gas exchange. Humans and land- dwelling vertebrates do this by expanding the lung cavity to draw air in, and reducing it to force air out. Worms conduct gas exchange through their moist skin, but do not actually breathe.

Sexually mature worms as identified by a clitellum.

Tiny rigid structures on most segments of earthworms which serve as brakes during movement. Known as setae, the patterns they form are a major distinguishing characteristic of earthworms.