Everybody’s seen earthworms; probably as a kid you used to pick them up and marvel at their sliminess (I know I did). I always thought they were kind of cute, but I know many people don’t agree with me. Still, I think we should learn about our little wormy friends, so let’s talk about earthworms!

Earthworms belong to the order Megadrilacea, though the exact classification of earthworms is under heated debate. It doesn’t help that there are over 6,000 species of earthworm, and that ‘earthworm’ is a common term, not a scientific one. Earthworms are found pretty much all over the world (though not in arctic or Antarctic areas), and like places that have lots of water.

800px-Earthworm
A nice adorable earthworm. Image source: Wikipedia

The size variation in earthworms is staggering: the smallest species is a paltry 10 mm long and 1 mm wide while the largest is a staggering 3 m long and 2.5 cm wide. I like earthworms, but the thought of a worm that big gives me the creeps. Earthworms are tubular, worm-like animals, divided into a number of different segments, which differ depending on the species. Depending on the species and the amount of damage done, some earthworms can regenerate segments that have been damaged.

Earthworms have pores covering their bodies which secrete a slimy substance to keep the worms moist. This helps the worms move through the soil, which is pretty important for a fossorial (burrowing) species. Worms maintain their shape through pressure; they have a chamber inside them called the coelom that is filled with fluid. When stressed, some species of earthworm can squirt this fluid, and the blue squirter earthworm is a master of this, being able to squirt its fluid 30 cm high.

Reproduction in earthworms is a private affair, occurring mainly at night. The worms come to the surface and then get down to business, locating one another through chemical signals. As hermaphrodites, earthworms possess both male and female organs, and both worms will exchange sperm with one another before separating. Once alone, the earthworm creates a ring around itself into which it deposits its eggs and the other worm’s sperm. The worm then worms its way out of the ring, which creates a little cocoon in which the little worms incubate. When they emerge, the babies basically look like adults, and become sexually mature after two to three months.

800px-Mating_earthworms
Two earthworms mating. The pink ring is the clitellum, which stores the worms’ eggs. Image credit: Jackhynes, via Wikipedia

Earthworms are detritivores, meaning they subsist on decaying plant and animal matter. This is very important for the ecosystem, as earthworms change dead organic matter into forms that plants are able to use, recycling nutrients. They also aerate and mix the soil they live in, and so are doubly useful for agriculture. Finally, earthworms are tasty food for many animals, and thus are probably some of the most important invertebrates around. Not too shabby for some little worms.

Advertisements