Spanish slugs have an annual life cycle. The adults are present in summer and subsequently generally are dying in late autumn. Each adult slug lays several clutches of eggs in the soil The juveniles hatch in the same year and overwinter. In early spring they can cause the first signs of damage, but maximum seasonal feeding and mobility occurs in summer. At the end of the summer, they reach sexual maturity and reproduce.
Possibly originating from Southwest France, during the last decades this invasive species spread its range and is now established almost everywhere in Europe.
Mainly reaches its highest densities in habitats disturbed by human activities, but also colonizes natural habitats to some degree.
The spanish slug is a horticultural pest in large parts of Europe, damage is mainly known from domestic gardens, vegetables, ornamental plants, strawberry cultures and oilseed rape fields.
Feeding on leaves and stems or seedlings of the spanish slug may destroy whole plants, especially if the growing point is damaged. Faecal and slime contamination to inflorescences and mature crops makes them unmarketable. The presence of live or dead slugs in harvested plants will lead to rejections.
The spanish slug causes most damage in domestic gardens or at margins of large fields, where hiding places are available.
The adult stages of the spanish slug in domestic gardens can be controlled by slug fences and collecting by hand. For the control of the younger stages, also on larger fields, a high tillage frequency is beneficial.
Mainly juveniles of the spanish slug are susceptible to natural predators, e.g. larger ground beetles, some birds, or nematodes. Adult spanish slugs seem to be better protected by the thick layer of mucus.
Biological Name
Arion lusitanicus auct., non Mabille, 1868 or Arion vulgaris Moquin-Tandon, 1855.
Both scientific names of this pest species are currently in use, as the taxonomic status is unresolved.
Common Name
Spanish slug
Other Common Name
Iberian slug, lusitanian slug
Appearance/Characteristics
A large, slender slug, 70 to 120 mm body length, a keel is absent. The pneumostome on the right side of the mantle is located in the anterior half oft the mantle. Spanish slugs often are uniformly reddish brown or brightly orange, whereas juvenile specimens show greater colour variation, often with a dark lateral stripe on either side. The mucus is colourless or pale orange.
Other Similar Species
Arion rufus, Arion ater
Based on external morphology, single specimens can be undistinguishable. An accurate identification may only be possible by dissection and investigation of the genitalia or molecular analysis.