While the term ‘worm’ can refer to any number of different animals, many of which have no relation to each other, here we will focus on the common earthworm. Though originally native to mainland Europe, the common earthworm is one of the most invasive species in the world and can be found in great numbers in North America, Australia, New Zealand, Iceland, South Africa, and Asia. While it is not the most numerous species of worm, it is often the most commonly seen due to their habit of coming to the surface after a rain or at night. They are also often the species used in biology classes for dissection.
Worm Life Cycle
Scientific & Common Names
Kingdom – Animalia
Phylum – Annelida
Class – Clitellata
Subclass – Oligochaeta
Order – Haplotaxida
Family – Lumbricidae
Genus – Lumbricus
Species – L. terrestris
Common Names – Worm, Earthworm, Lob Worm, Night Crawler, Dew Worm, Squirrel Tail
The nearly featureless brownish-red worms can be anywhere from 1-14 inches long, depending primarily on the environment. Their bodies consist of ringed segments called annuli which are covered with tiny bristles called setae. The translation of their Phylum name means ‘little rings’. The setae allow the worm to burrow through loose or wet soil, even though they have little strength. Worms have surprisingly complex systems, which is why they are often used in biology classes. They have five aortic arches, which are essentially hearts. They also have a complete digestive system, including an esophagus, gizzard, and intestines. They do, however, lack lungs and absorb oxygen through their skin. While popular myth holds that a worm can be cut into segments and those pieces will regenerate new worms, that is not the case. There are some studies into how much a worm can restore some minimal loss, but there is no real consensus on this ability.
All earthworms are hermaphrodites, meaning they contain both male and female reproductive organs. When mating, the earthworms will exchange sperm and later, after separating, they will fertilize their own eggs and leave a cocoon with the developing embryos. They gestate for 2-4 weeks and they the tiny but fully formed young worms emerge. They become sexually mature in 3-4 months.
Charles Darwin estimated that earthworms could move 100 tons of soil per hectare in a year, making them invaluable for soil aeration and fertilization. Earthworms feed mostly on the surface and at night – thus their common American name, night crawler. They consume leaf litter and other debris and then return to their underground burrows, where their castings help to fertilize the soil.
Surprisingly, worms were of special interest to Charles Darwin and he studied them extensively, even devoting his last published work to the invertebrates - The Formation of Vegetable Mould, Through the Action of Worms. Their evolutionary history is difficult to track since, as soft bodied animals, they leave little by way of fossils. Their earliest accepted ancestor is dated from 505 million years ago, during the Cambrian period, but it is possible that their lines dates much further back.
While the common earthworm is under no species-wide threat and is sometimes considered a pest when it competes with native species, there are some localized threats. In northwestern Europe, it faces serious predation by both the invasive New Zealand flatworm (A. triangulatus) and the Australian flatworm (A.sanguinea).
Fauna Britannica Hamlyn, London By S. Buczacki
University of Pennsylvania School of Arts and Sciences
The Formation of Vegetable Mould through the Action of Worms by Charles Darwin
Worms, Shadows, and Whirlpools: Science in the Early Childhood Classroom by Karen Worth
The Complete Guide to Working with Worms: Using the Gardener's Best Friend for Organic Gardening and Composting (Back to Basics) by Wendy Vincent