Earthworm

Although they are so inconspicuous, they are the superstars in the soil: earthworms eat plant remains and soil particles, turning them into valuable humus.

Characteristics

What do earthworms look like?

Earthworms belong to the order Lesser bristle and to the class Beltworms and to the phylum Ringletworms. Here you can find the common earthworm or dewworm (Lumbricus Terrestris) and the compost worm (Eisenia fetida). The common earthworm is nine to 30 centimeters long, the compost worm reaches four to 14 centimeters. Earthworms have a typical structure: their body consists of numerous segments. Four pairs of short, flexible bristles sit on each segment. The common earthworm is usually brown to red in color, the compost worm is red with yellowish ringlets.

Earthworms grow by forming new segments at a specific zone at the posterior end. Adult earthworms have up to 160 segments. The worm body consists of different layers: Under the outermost layer, the cuticle, lies a thin skin, the epidermis, in which sensory cells and glandular cells are embedded. With the help of these sensory cells, the worm can perceive light stimuli and touch. Below that is a layer of circular muscles and below that is a layer of longitudinal muscles.

At the head, the end is the mouth opening, which is arched over by the so-called head flap. After the mouth opens, there is the esophagus with the goiter and a gizzard. In this, the food is ground up with the help of grains of sand eaten with it. This is followed by the intestine, which runs through the worm to the anus.

Earthworms have a brain, the pharyngeal ganglion, and nerves and blood vessels that run throughout the body. They don’t have lungs: They breathe with their skin, which means they absorb oxygen through their skin and release carbon dioxide. In order for this skin breathing to work, the skin must always remain moist.

Where do earthworms live?

Different species of earthworms are found all over the world. Earthworms live several meters deep in the soil. They prefer temperatures of ten to 15 degrees Celsius and moist soil. They just don’t like very wet and boggy soil. There are an average of 100 earthworms per square meter of soil. The compost worm is only found in compost heaps.

What types of earthworms are there?

There are around 670 different species of earthworms around the world. About 46 species live with us. The best known are the common earthworm or dewworm and the compost worm.

How old do earthworms get?

Earthworms can live for two to eight years.

Behavior

How do earthworms live?

Earthworms are mostly nocturnal. During the day you can usually only find them when it has rained heavily. The animals can often also be spotted by the small ring-like droppings that they leave on the surface of the ground. Thanks to their circular and longitudinal muscles and their bristles, which they use to hook onto the ground, rainwarmers are good at digging through the ground and crawling forwards as well as backward. They contract the circular and longitudinal muscles and then stretch them again.

Their digging activity creates tubes in the ground that are lined and stabilized with mucus and excrement. The tubes can be up to 20 meters long and reach three meters or more into the ground. Earthworms aerate the soil and transport nutrients from bottom to top. On the other hand, they absorb the often acidic substances in the soil and neutralize them through their digestion. And they eat parts of plants and excrete them as nutrient-rich droppings – they transform the plant remains into valuable humus. In this way, they fertilize the soil.

In some earthworms, part of the body is lighter in color. This is due to a special ability: earthworms are very good at regenerating. If the rear end of the worm is severed by a bird’s beak, it will grow back. However, this piece is lighter in color and slightly thinner than the rest of the worm. Regeneration works best when the first 40 body segments are preserved. If more segments are missing – or those with the head and nerve center – the worm cannot regenerate. Splitting an earthworm in half does not create two new worms.

This ability to regenerate has a major advantage for the worms: if a bird grabs them, they can actively pinch off some segments. These then remain in the bird’s beak while the rest of the worm can flee. If the worm then regenerates a part of its body, it falls into what is known as body rigidity. Enemies such as moles take advantage of this by biting off the worm’s foremost segments and storing the subsequently immobile worms as living supplies.