Earthworms

Classification (systematic position) Source : INPN   Animal Kingdom Embranchement (Phylum) : Annelida Classe : Clitellata Subclass: Oligochaeta Ordre : Crassellitellata Under Order: Lumbricina

Morphological characteristics
Annelids with an elongated body, no legs (apodia), many segments (called rings) made up of many muscles, no skeleton. At maturity, a clitellum is apparent (bulge in the body). Setae are present but few throughout the body (Oligochetes) and are used for movement and clinging to soil particles. Worms have powerful muscles that allow them to burrow to great depths (up to 60 cm, sometimes 2 m) depending on the ecological category of the worm.

Life cycle
Earthworms reproduce actively in spring and autumn, but mainly when humidity is present and the temperature is between 12 and 25°C. Thus the manure and compost worm ( Eisenia fetida ) can reproduce often if these conditions are met and food is abundant. Earthworms are hermaphrodites and can therefore reproduce between two individuals. During mating, the clitellum serves to keep the two individuals together so that the exchange of male gametes can take place through the genital pores. The sperm are then stored in a spermatheca. Then, after copulation, the clitellum of the two individuals will allow the production of eggs (cocoons) in which fertilization will take place (the female and male gametes having been taken away during the creation of the cocoon). The cocoon will move along the body of individuals and grow to the anus and then be deposited in the ground. The cocoons will then hatch and give young worms which will reach sexual maturity in a few months (on average 3 months). Some earthworms like Lumbricus terrestris can theoretically live up to 6 years. However they are victims of strong predation and they often die young because they have no means of defence. An adaptation to this predation pressure may be the development of a rapid reproductive system.

Diet
Earthworms feed on vegetable waste and at the same time ingest soil depending on the ecological category to which they belong.

Natural predators or regulators
Worms have many predators: moles, hedgehogs, amphibians, birds and carnivorous arthropods.

Habitats
Earthworms look for moist soils but leave them if they are flooded. In times of drought and cold, they sink into the ground where they can become dormant in cubicles and then lose up to 50% of their water (mainly in winter and summer).

Three ecological categories of earthworms have been defined by scientists based on their lifestyles (habitat and roles).
Epigeal: these worms live on the surface mainly in rich organic environments such as litter made of dead leaves, or compost. They are generally small in size and pigmented allowing them to blend into the environment and hide from predators.
Anecics: they are large animals dark in front of the body. Their head is tapered and their tail is a spearhead. These worms dig essentially vertical galleries that can go up to 1m deep (important for water and air infiltration in the ground). They mainly come out at night to eat leaves from the litter on the ground surface. They fill their galleries with surface droppings (called castings because they are shaped like little towers). Some species can be epigeal because they are epigeal at the initial juvenile stage then anecic thereafter, or because of adaptation to a particular soil. Lumbricus terrestris and Aporrectodea giardi are examples.
Endogenous: these worms live in the ground, fleeing the light from the surface of the ground. They feed on soil and throw droppings into their galleries which are mainly horizontal. They are small and faintly colored worms. Earthworms live in all types of soil. There are 3 main classes of earthworms: the epigeic which live in the first centimeters of the ground, the endogenous which live in depth and the anecic which move from the surface to the depth.

Interests in the garden
Earthworms greatly increase the fertility of a soil by mixing the soil and the organic matter that they reject in the form of droppings rich in plant nutrients (castings). Earthworms also allow the activation of micro-organisms and therefore the acceleration of the recycling of organic matter. We use the image of sleeping beauty to better understand worm-bacteria mutualism

Worms constitute the largest animal biomass on the continents. The work of earthworms, whatever their ecological category, has significant effects on the soil:
- increase in porosity which improves the natural drainage and aeration of the soil (regulation of the water cycle)
- mixing action which causes a rise of mineralized soil and the burial of organic matter
- droppings (castings) are rich in nutrients and improve the structure of the soil
- their galleries constitute preferential paths for roots and can counterbalance, at least partially, compaction by agricultural machinery
- worms are an important food source for many carnivores and insectivores
- they accumulate certain pollutants from the soil

Did you know ?
Earthworms do not multiply if they are cut, only the part upstream of the clitellum, the part which has the most vital organs, can allow survival (quite rarely) by making new rings. The other part dies.

We can sample more rigorously the earthworms present in the soil on a surface of 1m² thanks to a protocol using mustard dissolved in water (OPVT).

When it rains a lot, the anecic earthworms (the biggest ones) come out of the ground to avoid drowning because the galleries are filled with water in which the oxygen necessary for the cutaneous respiration (through the skin) of the worms escapes. rare fact. They therefore come to the surface to capture the oxygen in the air through their skin.