Arion subfuscus

Arion subfuscus is native to the Paleartic (Beyer and Saari, 1978) and has been introduced to northeastern North America, where it ranges from eastern Canada to South Carolina, and as far west as Indiana. In Europe its range has expanded to include the northwestern, central, and eastern regions (Pinceel et al. 2005). (Beyer and Saari, 1978; Pinceel, et al., 2005)

Habitat use by the terrestrial gastropod Arion subfuscus varies seasonally. In fall A. subfuscus can be found foraging in moist plant debris and small crevices in the soil. As winter approaches, it usually moves deeper into the soil, returning to the leaf litter in spring. In summer A. subfuscus must find adequate shelter to prevent desiccation (Beyer and Saari 1978). (Beyer and Saari, 1978)

Arion subfuscus is a terrestrial slug. Like most slugs A. subfuscus has a tough body covered in mucus and lacks a visible shell. A. subfuscus individuals will have one of four color groups: reddish brown, black, orange or yellow, and lateral or mantle bands may or may not be present (Beyer and Saari, 359).

Arion subfuscus is a pulmonate gastropod and thus lacks gills but instead has a lung developed from the mantle cavity. The lung is open to the outside by a small pore called the pneumostome, which permits air exchange but limits water loss. The mantle sits on top of the body and lung. Internal shells are very reduced and present only as calcareous grains under the rear part of the mantle (Nichols, Cooke and Whiteley, 62). (Beyer and Saari, 1978; Nichols, et al., 1971; Pearse, et al., 1987)

Arion subfuscus generally has an annual life cycle where eggs hatch in autumn and adults die in summer. This can vary, however, depending on geographical location and habitat (Beyer and Saari 1978). Adults lay eggs which hatch directly into small juvenile slugs. The slugs grow slowly during the first few months, followed by rapid growth resulting in sexual maturity. During the period of rapid growth, the hermaphrodite gland becomes enlarged and the ratio of gland weight to body weight reaches a maximum as body weight reaches a maximum in the spermatozoon stage. During the reproductive stage, body weight remains constant but the hermaphrodite gland decreases in size as the slugs move into post-reproductive phase (Barker 1991). (Barker, 1991; Beyer and Saari, 1978)

Arion subfuscus is hermaphroditic and can both self- and cross-fertilize, depending on the conditions and habitat stability (McCraken and Selander 1980). (McCraken and Selander, 1980)

During copulation slugs exchange sperm through their protruding genitalia. Fertilization is internal, and several days after mating the slug will lay hundreds of eggs in the soil. Most adult slugs die soon after breeding and there is no parental care (Barker 1991).

In Arion and other genera, some individuals engage in apophallation: during sperm transfer male genitalia can become entangled. In such a case, the slugs may bite off each others penises to free themselves. Following apophallation the slug effectively becomes a female and never regains male functioning. (Barker, 1991)

Species such as A. subfuscus that belong to genus Arion lay their eggs in clusters in the soil. Although the eggs are left alone and there is no parental care, the eggs are chemically protected by a diterpene called miriamin. This chemical is a caustive agent that prevents the eggs from being eaten or damaged (Schroeder et al. 1999). (Schroeder, et al., 1999)

A. subfuscus is an annual species with a lifespan ranging from 8-12 months. Arion slugs generally hatch sometime between autumn and winter. They typically undergo a period of slow growth during winter followed by a period of rapid growth culminating in reproductive maturity. Slugs usually die post reproduction, but this can vary depending on the conditions and geographical location (Barker 1991). (Barker, 1991)

Arion subfuscus utilizes a muscular “foot” to creep slowly through vegetation and litter. A. subfuscus is most active during dusk or night to avoid desiccation(Beyer and Sarri 1977). (Beyer and Saari, 1978)

Home range is relatively confined because of its generalist feeding habits and avoidance of dessication (Beyer and Saari 1978). (Beyer and Saari, 1978)

In general terrestrial gastropods have poor ability to perceive objects by vision, and have little or no auditory perception. The primary sense used in perception is smell. The olfactory organs on a slug are located at the tips of the tentacles. The 4 tentacles can regenerate if they are removed and the olfactory organ will regenerate with it. Slugs also have chemoreceptors to detect toxins. The chemoreceptors are located on the lips. They eyes of the slugs are not primarily for vision. They are thought to be used to perceive light and to set its circadian rhythm (Barker, 2001). (Barker, 2001)

Arion subfuscus uses its radula to scrape and consume its food (Pearse et al., 1987). It appears to have a broad diet which includes fungi and decaying plants as major components, but also yellowed foliage, exposed plant parts, animal feces, insect larvae, dead or injured earthworms, and algae. A. subfuscus was observed foraging 6 m from the ground on tree trunks (Beyer and Sarri, 1977). (Beyer and Saari, 1978; Pearse, et al., 1987)

Arion subfuscus is preyed upon by a wide variety of organisms including insects, amphibians, reptiles, birds and small mammals (Martin, 2000). (Martin, 2000)

Arion subfuscus is an example of a generalist species and has been found living in woodlands, arable lands, edge habitats, and around human habitations. They can survive in a variety of soils and microhabitats including soil, plant litter and vegetation. As generalist herbivores, slugs could be a major factor in limiting the geographical ranges of plants (Scheidel and Bruelheide, 1999).

Because terrestrial slugs store environmental chemicals in their bodies, these toxic residues may be passed along the food chain and ultimately affect the biodiversity of an ecosystem (Martin, 2000). (Martin, 2000; Scheidel and Bruelheide, 1999)

A. subfuscus and other slugs are potentially useful as indicators of metals and other contaminants in the environment. (Martin, 2000)

Slugs are significant agricultural pests. Given its continued growth in abundance and range, Arion subfuscus is among the most important slug pests in North America (Frank 2003). (Frank, 2003)

A. subfuscus is not listed as endangered, threatened, vulnerable in any part of its range.