There before my eyes two earthworms were coupled; each anchored in a different hole and joined above ground at other end. As I approached, I broke the mood apparently and the time for ‘worm love’ was gone as each rapidly retreated into its respective burrow.
The earthworm is a well-known part of our local ecosystems, and is in fact found worldwide, with between 3,000-7,000 species, depending on which source one checks. The first thing one learns at an early age is these critters need to be kept moist, a feat they accomplish by living in damp ecosystems. They can vary tremendously in size depending on species. Here in North America, the largest worms can be 30 cm long, while some tropical species can reach 300 cm. Wow that’s almost 10 feet!
They breathe through their skin and cover themselves in mucous to assist the transfer of oxygen into the blood stream. The biology of worms is unique and truly fascinating. Looking, at first, like a long pink tube with no front or rear end, careful study shows the body is segmented and has tiny bristles along most of it's length, to aid movement. It has a mouth which can be withdrawn and concealed or expanded to sample the organisms on which it feeds. Inside it has multiple hearts, up to 10 in some species. Unlike any other invertebrate, they have hemoglobin in the blood just like us.
Mostly just a digesting machine, much of the body is made up of an elongated stomach, with a gizzard and crop to grind and store food respectively. They don’t have eyes but can ‘see’ variations in light intensity, through structures called Light Cells of Hess, but they mostly rely on vibration to sense the presence of predators, called vermivores, meaning “worm eaters.”
Earthworms can live over 6 years in the wild, an incredibly long time for an invertebrate. Food consists of: organic matter in soil, such as decaying roots and leaves; augmented with living organisms, such as nematodes, bacteria and fungi; and the decomposing remains of other animals. Voracious feeders, in one day, they can eat 1/3 of their body weight.
Reproduction is most fascinating. Earthworms are hermaphrodites, meaning they have both male and female reproductive organs. As the worms couple, they interlock and the sperm of each are passed to the other, to fertilize the eggs inside a mucous tube. This tube eventually becomes a capsule containing the fertilized eggs, which is shed and remains in the soil until the baby worms hatch. Not prolific breeders, each worm will produce 4-160 offspring per year, depending on the species.
When studying worms we have all noticed the “bump” part way along the body, but what is it? It’s called a clitellum, and it contains a gland which secretes the mucous that forms the cocoon mentioned above. It is a saddle-shaped, swollen area on the back and will only be found on sexually mature worms. Adverse environmental conditions can interrupt the sexual cycle and old age can shut it down entirely. Interestingly, species living deep in the soil produce fewer young, as there are fewer predatory pressures for them. Several species can self-fertilize, (i.e. parthenogenesis) so a mate isn’t always necessary to reproduce.
One question that has always fascinated me is “can earthworms regenerate themselves if injured?” The short answer is “yes”, but there are a few riders attached. Only the head end (end closest to the clitellum) can be regenerated, and even then at least half of the body must remain intact for this to happen, and the clitellum must not be damaged.
So if you’ve ever wanted to study the fascinating sexual reproduction of worms, now is the time, things are happening out on the turf!
Geoff Carpentier is a published author, ecotour guide and environmental consultant. Visit Geoff on-line, at www.avocetnatureservices.com and on LinkedIn and Facebook.