Some earthworms have the facility to replace or replicate lost segments, including some that can regenerate a new head.
Most polychaete worms have separate males and females and external fertilization.
Worm is a common name for any of a diverse group of invertebrate animals with a flexible, soft, typically long and slender body and generally without obvious appendages.
Earthworms aerate and mix the soil, help with composting (converting dead organic matter into rich humus), and convert soil particles into accessible nutrients.
Worms vary in size from less than 1 millimeter (0.04 inch) in certain aschelminths to more than 30 meters (100 feet) in certain ribbon worms.
Other worms are used as bait for recreational fishing and as indicators for monitoring the health of environments.
About 2,700 of the invertebrates known as worms are earthworms.
Hence, "helminthology" is the study of parasitic worms.
Worm species differ in their abilities to move about on their own.
The most common worm is the earthworm, a member of phylum Annelida.
Other invertebrate groups may be called worms, especially colloquially.
Worms may also be called helminths, particularly in medical terminology when referring to parasitic worms, especially the Nematoda (roundworms) and Cestoda (tapeworms).
Earthworms are hermaphrodites but generally cannot fertilize their own eggs.
The worms may be pelagic, surface dwelling, or benthic, burrowers or tube dwellers, mobile or sessile.
Many worms have sense organs that can detect environmental change.
Some worms living in the ground help to condition the soil (such as annelids, aschelminths).
Arrow worms (Chaetognatha) are a major component of zooplankton worldwide.
Metaphorically, worms are used as a metaphor of putrefaction, death taking over life, and death itself, an image of hell.
Many worms thrive as parasites of plants (for example, aschelminths) and animals, including humans (for example, platyhelminths, aschelminths).
Hermaphroditism, the condition in which a single individual possesses both male and female reproductive parts, is common in many groups of worms.
Worms live in almost all parts of the world including marine, freshwater, and terrestrial habitats, as well as brackish and arboreal environments and the seashore.
Animals grouped as worms usually have a cylindrical, flattened, or leaf-like body shape and are often without any true limbs or appendages.
Several other worms may be free-living, or nonparasitic.
Earthworms in general have been around for 120 million years, evolving during the time of the dinosaurs.
There exists a mythological image of a never dying worm who is eternally eating dead people (Ligeia).
When an animal, such as a dog, is said to "have worms," it means that it is infested with parasitic worms, typically roundworms or tapeworms.