Earthworms

Earthworms

Earthworms are among the most familiar yet least celebrated inhabitants of any land,  transforming the ground beneath our feet. In the United Kingdom there are about 30 native species, ranging from the tiny Enchytraeus pot‑worms barely a centimetre long to the deep‑burrowing Lumbricus terrestris — the common garden lobworm, which can stretch to 30 centimetres and descends a metre or more into the soil. They fall into three distinct lifestyles: shallow litter dwellers that live in the surface layer eating decaying matter; topsoil workers that mix organic material into the upper layers; and those deep vertical burrowers that pull leaves down from above and drag mineral soil up from below, slowly turning the earth over, grain by grain.

Hermaphrodites

Every earthworm is both male and female — a true hermaphrodite — carrying both sets of reproductive organs. When two meet, they exchange sperm with each other simultaneously, so both partners go away fertilised. Later, each forms a pale, thickened band near its head — the saddle — which slides forward along the body, picking up eggs and stored sperm as it goes, then slips free to seal itself into a tiny lemon‑shaped cocoon from which one or two miniature worms eventually emerge. They move with elegant coordination: lengthening the front end by contracting circular muscles, anchoring it with tiny bristles called chaetae, then pulling the rest of the body forward by contracting longitudinal muscles — a rhythmic, wave‑like motion that allows them to glide through soil without displacing it. They breathe through their skin, which must stay moist at all times — hence their reluctance to venture out in dry weather — and under favourable conditions they may live for several years.

Darwin

Their contribution to the living landscape is immense. They aerate the soil with their tunnels, improving drainage and allowing roots to penetrate deeper; they mix nutrients from top to bottom, preventing fertility from leaching away; and their digestive systems break down plant material into forms that plants can readily take up. Charles Darwin recognised all this long before it became widely understood. In his later years he devoted decades to careful observation and experiment, measuring how much earth worms brought to the surface each year, how they buried stones and ancient buildings, and how they shaped the very face of the land. His findings were published in 1881 (the year before he died) as The Formation of Vegetable Mould through the Action of Worms, a work that sold beyond all expectation and remains a classic of ecological science. In its early days of publication it sold more rapidly than his book On the origin of species.

Invasive Flatworms

Not all worms in the UK are native. The most unwelcome arrival is the New Zealand Flatworm, Arthurdendyus triangulatus, a dark, ribbon‑like predator up to 20 centimetres long that glides silently through damp earth hunting exclusively for earthworms. It has no eyes, but tracks its prey by chemical scent, envelops it, and secretes digestive enzymes that dissolve the worm’s body before absorbing the nutrients directly — a gruesome process that leaves nothing but an empty skin. It arrived in the United Kingdom during the 1960s, hidden in the soil of exotic plants imported for botanical gardens, and has since spread across much of Scotland and northern England, thriving in cool, damp conditions that mirror its homeland. It reproduces without mating — each individual produces hard, black, shiny cocoons that survive even when the parent is killed — so a single flatworm can found an entire population. With no natural enemies here, it can wipe out local earthworm populations entirely, leaving the soil less turned, less aerated, and less fertile in its wake. some hears ago this flatworm was discovered in the tree nursery at Dun Coillich. In the UK the New Zealand flatworm first appeared in the Belfast botanic gardens in 1963 and then in the Edinburgh Botanic Gardens in 1965.

Giants Earthworms

In its native New Zealand, the flatworm is one part of a very different world — one where the earthworms themselves are giants. Some Australian and New Zealand species grow to well over a metre in length, thick as a thumb, living deep in ancient forest soils and emerging only at night or after heavy rain. They are relics of an ancient fauna that evolved in isolation, untouched by the ice sheets that repeatedly scoured the northern hemisphere.

No Earthworms -

Indeed, the story of earthworms and ice is one of the most remarkable chapters in the natural history of the northern continents. During the last Ice Age, glaciers advanced across much of northern North America, scraping the land bare and wiping out every earthworm as they went. For thousands of years after the ice retreated, the forests regrew — but they regrew without earthworms. Earthworms are notoriously slow at spreading. The leaf litter accumulated year upon year into a thick, spongy, acidic mat that decomposed slowly, held together by fungi and microbes rather than worms, creating a unique nutrient cycle that shaped the composition of the entire forest. This thick map of vegetation is called the duff and it helps retain moiture. Trees such as sugar maple and the magnificent northern oaks adapted to this slow, steady release of resources. Then, with the arrival of European settlers, European earthworms were brought in — in ship’s ballast, in soil around plants, in root‑balls from home — and they began to spread. Where they advance, they consume that protective layer of leaf litter far faster than the native system can sustain, altering soil temperature, moisture, fungi and nutrient availability — and in places threatening the very forests that grew up without them. The forests of New Jersey had 15,000 years to evolve without earthworms and now invasive earthworms introduced by people are upsetting the balance.

The human Influence

In the past few hundred years humans have mixed up the flora and fauna of the world, which had achieved a balance over millions of years. In some cases it will take millions of years for new balances to form.