Yes, that’s right — we will be talking about Lumbricus terrestris, more commonly known as earthworms, a species often overlooked or forgotten by many, which is why this fact sheet is important.

Context

Earthworms first appeared on Earth during the Precambrian period, approximately 600 to 700 million years ago, but they underwent significant development around 500 million years ago during the Cambrian. In the Paleozoic era, numerous physical characteristics emerged, particularly in their renowned digestive system, which is designed to break down organic matter in the soil. This process contributes to enriching the soil with nutrients, producing what is known as mull.

Description

Earthworms, or lumbricids, are invertebrates belonging to the phylum Annelida, which includes over 7,000 species, around 150 of which are found in France. Among the most common are Lumbricus terrestris, also called the common earthworm, as well as Lumbricus rubellus and Eisenia fetida. Some species are semi-aquatic, breathing air at the surface through a siphon and can live up to eight years. They withstand frost and drought by limiting their activity.

Earthworms are classified according to various characteristics, such as the position of their clitellum, their length, shape, number of body segments, and the morphology of their setae. Their digestive tract is complex, including a pharynx for sucking in food, a gizzard, and a crop where calcium carbonate is added by calcareous glands. The digested material forms casts, enriching the soil.

Among these species, Lumbricus terrestris is particularly remarkable. Native to Europe, this earthworm can reach 20 to 30 cm in length as an adult. It has a segmented, reddish-brown body and is easily identifiable by its clitellum, a widened region of the body used for reproduction. This worm prefers soils rich in organic matter and well-drained, and is commonly found in gardens, meadows, and forests.

Each segment bears four pairs of short ventral setae, or a full row of setae in some tropical species. The size and shape of these setae vary according to their lifestyle and mode of movement. The first two segments, where the mouth is located, as well as the last segment, where the anus is situated, lack setae.

Additionally, another remarkable fact about their anatomy is that Lumbricus terrestris has an efficient circulatory system with several pairs of lateral hearts that ensure blood circulation throughout the body. Their metabolism is adaptable, slowing down during periods of cold or drought to enter a state of lethargy. Movement is achieved through asynchronous contractions of the longitudinal and circular muscles.

Lifestyle

In terms of reproduction, Lumbricus terrestris is hermaphroditic and can reproduce through parthenogenesis, without mating, by producing cocoons containing up to twenty eggs. The larvae that hatch are capable of independent life from birth. Finally, the earthworm is an essential soil agent, contributing to the decomposition of plant and animal debris and thereby facilitating nutrient cycling in ecosystems.

Importance and Threats

Earthworms, particularly Lumbricus terrestris, play a crucial role in terrestrial ecosystems by digesting and mixing the soil, thereby improving soil fertility. Lumbricus terrestris is capable of creating deep burrows, which aerate the soil and facilitate water infiltration as well as root access to oxygen. They secrete drilodefensins, substances that allow them to digest leaf tannins, and they respire through their skin, requiring a consistently moist environment.

The role of earthworms in agricultural systems is essential. They recycle manure applications, and their presence can increase the productivity of crops such as soybean and maize. Moreover, the burrows they create form an underground network that benefits other species. However, earthworms face numerous threats, including intensive agriculture, which has drastically reduced their populations, and the invasion of exotic species such as flatworms, which severely disrupt local ecosystems.

In areas where organic or semi-direct agriculture is practiced, earthworm populations are more abundant. Nevertheless, even these practices can be compromised by the use of certain treatments, such as Bordeaux mixture, which negatively affects these invertebrates. It is therefore crucial to implement protective measures to preserve these indispensable “soil workers” in order to maintain ecosystem health and agricultural productivity.

Earthworms are also a “preferred food” for many species: blackbirds, woodpeckers, sparrows, geckos, toads, frogs, arthropods, ants, and more.

Source

Les vers de terre (Lumbricinae) | Humanité et Biodiversité (humanite-biodiversite.fr)

Occurrence search (gbif.org)