meet the tiger worm and the night worm

Most people are familiar with earthworms, but probably give them little thought. Some think they are “good for the soil.” Others look at them with disgust, thinking of slimy animals associated with decomposition. But these alien-looking animals are extraordinary, controlling the foundations of life from their subterranean world.

Earthworms soil engineering that grow the food we eat and the flowers we love to look at. Indeed, they are major factors in forming the soil.

This earthworm intestine is a bit like a biological reactor in which numerous processes take place. The combination and processing of organic matter and mineral soil produces earthworm excrement (feces) both underground and above ground, which increases soil fertility. The burrows in the soil also allow water and air to circulate freely.

Rain Worms

Earthworms are not only imperative to the ecosystem, they are also fascinating animals.

Anyone who ventures out in the spring or fall after a night of rain can find dying earthworms on the strenuous ground. People sometimes think that these animals have left their burrows to avoid drowning, but that’s not even close to true. With no lungs or gills, earthworms breathe through their skin. Our lungs disperse oxygen from the air we breathe, but oxygen can just as easily diffuse through an earthworm’s skin from the water. Earthworms can live underwater for days.

So why do they come to the surface of the soil when it rains? Well, they most likely disperse and find new places live away from close relatives to avoid incest. The vibrations of raindrops encourage them to come to the surface – soggy ground is easier to walk on than droughty ground.

Night provides some protection from predators. The worms we see on the pavement the next day are those that have not found a recent burrow. Some predators of earthworms exploit this behaviour by ‘foot shaking’. Seagulls are a perfect example and will stamp their webbed feet on humid grass areas to trick the worms into coming out into the open, believing it is raining. This technique works very well.

Scientists have identified 6,000 species of earthworms, about 30 of which live in the UK. They can all be divided into three groups. The first live in organically wealthy material, such as a compost heap. These include the tiger worm or brandling (Eisenia fetida) and perfectly chop up materials such as vegetable peelings.

Other, unpigmented earthworms feed in the soil and dig horizontal burrows close to the soil surface. These include: grey worm (Aporrectodea caliginosa).

The third group consists of larger, deeply burrowing worms (about a meter below the surface), such as the dew earthworm or the night earthworm (Lumbricus terrestris). They utilize their mouths to pull leaves into their eternal, vertical burrows.

The activities of these groups of earthworms benefit each other. For example, the foraging and digging of earthworms enriches the soil that grey earthworms eat. In addition, all earthworms have sophisticated interactions with soil microorganisms, such as bacteria and fungi, which are bountiful in their feces.

Finding a partner

All earthworms are hermaphrodites (have both male and female reproductive organs), but some produce teenage from unfertilized eggs. Most mate underground, but some, including the earthworm, mate on the soil surface because their vertical burrows prevent them from meeting underground.

Scientists have observed interesting behavior above ground, which takes place before copulation, when there is a mutual exchange of sperm (each fertilizes the other). In worms, such as the earthworm, two worms “visit” the burrow of their potential mate with their heads, while they keep their tails in their home burrows. Each of them can stretch a great distance (about 30 cm).

Visits to burrows can last from 30 seconds to several minutes. Visits are made in both directions before copulation, which takes place in opposite directions and can last three hours. Further studies have shown that only worms similar size tend to mate. They deduce the size of a potential mate by sensing the entrance to his burrow.

As hermaphrodites, it is in the interest of each worm to be both a successful “mother” and “father.” This increases the number of teenage and thus the survival rate. All worms produce cocoons from their “saddle” (a raised area on their body). They create a tube of protein that slides down their front after filling it with their own eggs and stored sperm from their partner. They then lay it underground as a lemon-shaped cocoon.

It hatches after a few weeks, depending on the species. Some species of worms surround the cocoon with leaf fragments as a first meal for their teenage.

During copulation, earthworms join together by piercing each other’s skin with pili (hair-like projections on the skin), which allows sperm to flow between them along the groove.

After copulation, the two worms separate, retreating into the burrow, “dragging” each other, pulling these bristles from the other’s skin. If they are not of equal size, one would completely pull the other out of the burrow and prevent it from returning, and thus be eaten by the predator.

Soil Drainage Strategies

Earthworms have evolved a mucus-coated skin that retains moisture and makes moving through the soil smoother. However, as soft-bodied, water-rich organisms, they are at the mercy of soil conditions. In unfavorable soil conditions, such as when the soil becomes too droughty (in summer) or too frigid (in winter), earthworms resort to survival strategies, has developed over thousands of years.

These include waiting at the bottom of a deep burrow, where the soil is wetter, and then going into a dormant state, curled up in a mucus-lined chamber in the soil (a form of hibernation).

Earthworms have evolved to produce cocoons that can remain dormant until conditions improve. The cocoons hatch when the soil is soggy and balmy, and the petite worms that emerge reach maturity, which can take up to a year in some species. With climate change occurring and predicted to worsen, earthworms face an uncertain future.

This should worry every single one of us – our future is closely linked to the future of earthworms.