Orange red slug, what is this species?

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Born 350 million years ago, or rather its ancestor, the orange-red slug or Arion rufus is the most common slug in France and Europe. Who is the orange red slug? What does she eat? What is its use for nature? Discover with us the particularities of this gastropod.

Arion rufus, color and distribution area

Recognizable by its red coat covered with folds on its back and sides, the Great Loach has been able to colonize vast areas of distribution. A common gastropod mollusk in central and western Europe, this slug which likes to leave traces of its passage on the ground through very sticky mucus also likes moors, wet meadows and forests. Absent in Scandinavia, the species is gradually being supplanted in our gardens by the southern loach or Arion lusitanicus.

If the red orange color is the most common in this terrestrial mollusk, its color varies from yellowish white to yellow, from brown to black and of course from brick red or orange red. These variable shades have led to it being described under several species. Arion Ater, the black form, and Arion rufus, with the red color, are one and the same species.

How to recognize the Great Loach?

If color does not allow you to precisely determine the species of slug that you catch nibbling on your young shoots, other physical aspects can help you:

The adult has no spots or bands; The back and sides are marbled with deep wrinkles; The skin has a bumpy appearance; The pedal sole has a lighter color than the rest of its body; The respiratory opening, located at the lower right edge, is large, making it clearly visible.

Spread out at full length, our pretty orange-red common slug can measure up to 15 cm long. More generally, the adult does not exceed 12 cm.

What does the orange red slug feed on?

A lover of freshness and especially humidity, you will most often encounter it at night, or during the day when it rains. The Great Loach tends to move at night, crawling using its sole to find food that will feed it. Like many slugs, its body made up of 85% water, constantly seeks to renew it by absorption:

With his skin; Through food; By hydrating.

Its varied diet allows it to feed on plants as well as carrion – earthworms, insects -, excrement, green waste and sometimes paper! It owes its unpopularity with gardeners and lovers of beautiful gardens to its pronounced voracity for young shoots and plantings in vegetable gardens and flowerbeds. Stems, buds, flowers, fruits, seedlings, plantlets, our charming gastropods can devour half their weight during the night.

A short life for our voracious vegetable gardeners

Covered in a hole in the ground or hidden under a pile of wood, a tile or a board with hygrometry favorable to gastropods, it is in spring or autumn that the orange-red slug mates. Hermaphrodites, slugs practice cross-fertilization. The two male partners exchange their spermatozoa in a veil of mucus or spermatophores. Each hosts the microgametes of the other, then when they transform into females, fertilize their macrogametes with the preserved sperm. Laying occurs 15 days to several weeks after copulation and each individual will lay up to 500 eggs. These come in packs of 10 to 50 eggs and are laid under dead leaves or in a hole dug in the ground. Hatching, which depends on temperature and humidity conditions, will see the birth, within 3 weeks to 3 months, of small transparent slugs ready to embark on their gastropod life.

The lifespan of the Arion rufus slug depends on weather conditions. It can thus live for a year or 18 months when drought or frost do not get the better of this cold-blooded mollusk. When winters are harsh, the slug burrows underground at 5°C.

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