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Kerry slug

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Kerry slug
The right side of a dark slug with yellow spots, head to the right
Photo of dorsal view
Drawing of right side view
Drawing of right side view
Scientific classification edit
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Subclass: Heterobranchia
Infraclass: Euthyneura
Superorder: Eupulmonata
Order: Stylommatophora
Family: Arionidae
Genus: Geomalacus
Subgenus: Geomalacus
G. maculosus
Binomial name
Geomalacus maculosus
Allman, 1843[2]
Geomalacus maculosus map.png
Distribution map for the species. It shows the "Lusitanian" type of disjunct distribution, but not the recently discovered Co. Galway population.

The Kerry slug or Kerry spotted slug (Geomalacus maculosus) is a species of terrestrial, pulmonate, gastropod mollusc. It is a medium-to-large sized, air-breathing land slug in the family of roundback slugs, Arionidae.

Adult Kerry slugs generally measures 7–8 cm (2.8–3.2 in) in length; they are dark-grey or brown with yellowish spots. The internal anatomy of the slug has some unusual features and some characteristic differences from the genus Arion, also part of Arionidae. The Kerry slug was described in 1843—later than many other relatively large land gastropods present in Ireland and Great Britain—a indication of its restricted distribution and secretive habits.

Although the distribution of this slug species includes south-western Ireland—including County Kerry—the species is more widespread in north-western Spain and central-to-northern Portugal. It is not found in locations between Ireland and Spain. The species appears to require environments that have high humidity, warm summer temperatures and acidic soils with no calcium carbonate. The slug is mostly nocturnal or crepuscular but in Ireland it is active on overcast days. It feeds on lichens, liverworts, mosses and fungi, which grow on boulders and tree trunks.

The Kerry slug is protected by conservation laws in the three countries in which it occurs. It is now known to be less dependent on sensitive, wild habitats than when these laws were introduced. Attempts to establish breeding populations in captivity have been made to ensure the survival of this slug species but these have been only partly successful.


The Kerry slug is a gastropod, a class of molluscs that includes all snails and slugs, including terrestrial, freshwater and marine species. The Kerry slug, a member of the order Panpulmonata, is terrestrial; it breathes air with a lung. It is in the clade Stylommatophora, members of which have two sets of retractable tentacles, the upper pair of which have eyes on their tips. Its family is Arionidae, the round-backed slugs. The Kerry slug has no keel on its back, unlike the slugs in the families Limacidae and Milacidae. Many of its anatomical features are shared with species in the genus Arion, which is a more species-rich and widely distributed group of slugs within Arionidae. The Kerry slug is placed in the genus Geomalacus, which means "earth mollusc".

The Kerry slug's binomial name is Geomalacus maculosus, maculosus from the Latin word macula "spot", meaning "spotted".[6] The English-language common name is derived from County Kerry in the south-west of Ireland, where the type specimens that were used for the formal scientific description were collected. In 1842, a Dublin-based naturalist William Andrews (1802–1880) sent specimens he had found at Caragh Lake in County Kerry to the Irish biologist George James Allman. The next year, Allman exhibited them at Dublin Natural History Society and published a formal description of the new species and genus in the London literary magazine The Athenaeum.[7][2] The full scientific name, including the taxonomic authority, is Geomalacus maculosus Allman, 1843.

The species' binomial name is sometimes written as Geomalacus (Geomalacus) maculosus because the genus Geomalacus contains two subgenera; the nominate subgenus (subgenus of the same name) Geomalacus and a second subgenus Arrudia Pollonera, 1890. The Kerry slug is the only species in the subgenus Geomalacus contains one species, the Kerry slug; three species comprise Arrudia.[citation needed] The Kerry slug has been included in molecular phylogenetics studies since 2001.[8]


Three yellow and brown spotted slugs with faint dark bands and dark tentacles. Top drawing shows right side of slug, which is facing right, the other two show slugs that are facing left. Second one shows view from above with 4 long bands, third shows a larger darker slug with only two long bands.
Colour variation in three individuals, lighter and darker; the lower two having indistinct banding

The body length of adult Kerry slugs are 7–8 cm (2.8–3.2 in).[9] These slugs are difficult to measure accurately because of their unusual startle response. Kerry slugs can also elongate themselves within crevices up to 12 cm (4.8 in).[9] Official measurements of this species vary; Kerney et al. (1983)[10] give a range of measurements of 6–9 cm (2.4–3.6 in). The body of a fixed (preserved) adult specimen was 7 cm (2.8 in) long with a mantle length of 3 cm (1.2 in).[9]

Colour morphs of G. maculosus. Brown individuals are typically associated with woodlands; black individuals are found in open habitats such as blanket bog or heath.[11]

The body of the Kerry slug is glossy and is covered on the left and right sides with about 25 longitudinal rows of polygonal granulations—very small knobs with polygonal outlines. The slugs have two colour morphs, brown and black. In Ireland the black morph occurs in open habitats and the brown morph occurs in woodland; this correlates with the colours of the surroundings, suggesting camouflage. Experiments indicate the dark colouration is induced by exposure to light as the slug develops.[11] There is also variation in banding; on each side of the body there can be two bands: one band just below the summit of the back and the other band further down the side of the body. When these bands are present they usually extend the whole length of the body and are overspread by numerous, ovoid yellow spots that are distributed approximately in five longitudinal zones.[7]

The tail end of slug showing a small triangular area in the middle, with a deep groove on either side right above the foot
The caudal end (tail end) of the body showing supra-pedal grooves and triangular caudal mucous pit
The tail end of slug has transversal ridge on its surface
Right view of the tail end of the body.

Behind the animal's head is the shield-shaped outer surface of the mantle, which is about a third of the length of the body when the slug is actively crawling and thus extended; when the slug is stationary and contracted, the shield is about half the length of the body. The front of the shield is rounded and its rear is bluntly pointed. The surface texture of this area resembles the underside of undyed leather; it is spotted with pale, buff or light-coloured spots that are similar to those on the body but are more uniformly distributed.[7]

The foot fringe, a band of tissue around the edge of the foot, is not distinctly separated; it is very pale and somewhat expanded and has indistinct lines on it.[7] The sole of the foot is pale grey-yellow and is divided into three indistinct bands; the mid-area is somewhat darker and more transparent than the side bands.[7] There is a caudal mucous pit situated between the foot and the body on the upper surface of the tip of the tail. The pit, which collects extra mucus, is inconspicuous, triangular and opens transversely. The mucous pit often carries a transparent, yellowish ball of mucus.[7]

The Kerry slug's upper tentacles are smoky-black or grey, short and thick with oval ends, and have eye spots at their tips. The genital pore or opening lies behind and below the right eye tentacle.[12] The lower tentacles are pale-grey and translucent.[7] The skin mucus is usually pale yellow and varies in viscosity. The locomotory mucus is tenacious and usually colourless but is sometimes yellow because of mixing with body slime.[7]

Internal anatomy[edit]


Most land slugs have, within the mantle, the remnants or residue of what was, in the evolutionary past, a larger external shell. In most slugs, this remnant takes the form either of a small internal shell (a thin shelly plate), or a collection of calcareous (chalky) granules. In this species there is an internal shell or shell plate which resembles that found in land slugs of the genus Limax. In other words, the shell plate in this species is oval in shape, solid, and chalky, with a transparent conchiolin (horny) base. The shell plate is usually somewhat convex above and concave beneath, with a few indistinct concentric lines of growth, and is covered outwardly with a very thin transparent periostracum (a protein layer), and with the nucleus (the oldest growth part) situated near the front. In young Kerry slugs the shell is very thin and convex, abruptly cut off behind, and with an extremely thin layer that projects in front and contains minute granules.[7]

The shell plate has been drawn differently by authors, but do at least show that it is a solid plate:

A roughly oval shell plate which is slightly domed and slightly irregular on the surface, with very few distinctive features
The internal shell as drawn by Taylor in 1907
A roughly oval shell plate with slightly irregular shape and slightly irregular on the surface, with very few distinctive features
The internal shell as drawn by Godwin-Austen in 1882
Photograph of internal shell of G. maculosus (dorsal view).

Various organ systems[edit]

Heart surrounded by tringular kidney. One retractor muscle is depicted on the right and two ones are one the left.
Anatomy viewed from below with frontal edge of mantle on the top. Heart (red) is surrounded by renal organ (yellow). Retractor muscles (blue) include retractor muscle of left eye tentacle (depicted on the right), retractor muscle of right eye tentacle and retractor muscle of odontophore (both on the left).
A double structure of two ganglia, with six nerves branching off
The cerebral ganglia, a central processing area which is equivalent to the brain within the nervous system of the slug

The circulatory and excretory system are closely related, in that the heart is surrounded by the triangular kidney. The kidney has a lamellate (layered) structure and it has two ureters. In this slug species, the ventricle of the heart is directed towards, and is very close to, the anal and respiratory openings. The ventricle of the heart is further away and further back than it is in species of the related genus Arion, the type genus of the family Arionidae.[7]

The gland above the foot, the suprapedal gland, is deeply imbedded in the tissues, and reaches far back. The cephalic (head) gland known as the Semper's organ is well developed, and shows as a pair of strong flattened lobes. The salivary and digestive glands are the same as those found in Arion species, but the vestigial osphradium (kidney-like structure) within the mantle chamber is more distinct than it is in Arion species.[7]


As for the various muscles within the slug, the cephalic retractors (muscles for pulling in the head) are very much the same as they are in Arion species. The right and left tentacular muscles, which pull in all four of the tentacles, divide early for the upper and lower tentacles, but only the muscles of the ommatophores (the muscles of the two upper tentacles, which have eye spots) are darkly pigmented. The right and left muscles that pull in the eyespot tentacles are attached at the base to the back edge of the mantle, on the right and left respectively. The pharyngeal (throat) retractor muscle is, as usual, furcate (split) for attachment to the back of the buccal bulb (mouth bulb), and the root of this muscle is fixed on the right side of the body, just behind where the right tentacular muscle is attached.[7]

Reproductive system[edit]

The Kerry slug is a hermaphrodite, as are all other pulmonates. Various authors have depicted its reproductive system: Godwin-Austen (1882),[13] Sharff (1891),[12] Simroth (1891, 1894),[3][14] Taylor (1907),[7] Germain (1930),[15] Quick (1960)[16] and Platts & Speight (1988).[17] Platts & Speight [17] considered the depiction by Godwin-Austen (1882)[13] to be the most accurate of those by earlier authors; others depicted the atrium too short.

The ovotestis (a combination of ovary and testis) is small, compact, and darkly pigmented. The hermaphroditic duct (for sperm storage) is very long and greatly convoluted, and ends in a small spherical seminal vesicle. The albumen gland (which produces albumen for the eggs) is elongated and shaped like a tongue. The ovispermatoduct (down which both eggs and sperm pass) is very much twisted. This turns into the free oviduct after the vas deferens (carrying the sperm) branches off. The free oviduct is rather long and thin, without any enlargement.[7] It opens into the atrium (see below) near the genital pore, where the muscular atrium is greatly but irregularly enlarged and connected to the oviduct by muscle fibres.[7]

The vas deferens is very long, complexly twisted, and rolled up in a bundle. The bursa copulatrix (for digesting spermatophore and sperm; earlier literature refers to this as the spermatheca) is globular, with a short bursa duct. There is a long retractor muscle from the bursa duct, its other end being anchored right near the tail of the slug at the midline. The vas deferens and the bursa duct open nearly together into the far extremity of the atrium (the duct into which both the male and the female systems open and which connects to the outside via the genital pore). A special feature of the genus Geomalacus is that the atrium is extremely elongated.[17] The elongated portion of the atrium further from the genital pore than the insertion of the oviduct is termed the atrial diverticulum. The penis in Geomalacus has been lost together with its penial retractor muscle. The atrial diverticulum has been proposed to be the functional equivalent (analogy, homoplasy) of a penis, acting as a copulatory organ.[18] It is presumed that the bursa retractor muscle functions to retract the atrial diverticulum.[18]

Geomalacus maculosus has an atrial diverticulum longer than the bursa duct, while Geomalacus anguiformis has an atrial diverticulum shorter than the bursa duct.[17]

Godwin-Austen[19] noted that the part of the atrium just inside the genital pore (he called this region the "vagina") has a curious arrangement of flattened folds. The central part, situated close to the genital pore, has a pointed end. He compared this to the calcareous darts in other genera (he had just been describing such structures in the Asian slug genus Anadenus).

The uncoiled reproductive system of the slug, showing three blunt-ended sacs attached to one large duct and one much finer one
The reproductive system illustrated by Godwin-Austen (1882).[13] The large mass on the right is albumen gland, the mass on the lower part right is the ovotestis, the oval shape at the left is the bursa copulatrix. Mantle edge and atrium is at the top.
Oval bursa copulatrix, connected with atrial diverticulum with atrium; fine tubular epiphallus; sketch of surrounding spermoviduct
Drawing of "male part" of the reproductive system. From lower left to upper left: genital pore, atrium, atrial diverticulum, bursa duct, bursa retractor muscle, bursa copulatrix. On the top right: epiphallus. Center: vas deferens. Lower right: free oviduct, spermoviduct.

Apparatus for feeding[edit]


The radula is a feeding structure found only in molluscs. Typically it is a small but strong ribbon-like structure with numerous complex rows of tiny teeth across it. The radula is situated inside the mouth.

In this species of slug, the radula is 8 mm (5/16 in) long and 2 mm (1/16 in) wide, and has 240 slightly curved transverse (crosswise) rows of denticles (tiny teeth). Each row of teeth is composed of one median tooth and 10 lateral and marginal teeth on each side. The median teeth are small, and are clearly unicuspid (having one cusp), though they are slightly shouldered. The lateral teeth are bicuspid (having two cusps) but the admedian (next to the middle) teeth are noticeably larger than the median row, and the mesocone (an extra protrusion in the middle of the tooth) is well developed. There is however, no distinction between the lateral and marginal series except that the ectocone (extra little side protrusion) present on the admedian teeth recedes in position and slightly diminishes in size in the succeeding teeth up to about the twentieth row on the radula, but in the marginal series, the ectocone gradually grows in size and importance as the margin is approached, while the mesocone becomes almost correspondingly diminished, the outermost teeth showing a more embryonic (more like that of an embryo) character.[7]

A complete row of 21 teeth or denticles, increasing in size towards the middle but with a small central tooth. The teeth are labelled with numbers or letters according to a conventional system of radula labelling.
One complete row of teeth in the radula
A parallel-sided broad arched structure with 8 raised ribs running from front to back
The jaw, which has broad ribs.

The jaw measures about 1 mm (1/32 in) from side to side, and is distinctly arcuate (arched) from front to rear, lunate (crescent-moon shaped) in shape, but very wide, with broad and slightly rounded ends. The jaw is solid, dark-brown and has about 10 broad flat ribs only in the middle part of the jaw. These ribs are absent or scarcely discernible on the side areas. Where the ribs meet the upper edge they sometimes form crenulations ( a scalloped effect) and may also produce the same effect on the lower edge of the jaw. In other individuals the ribs extend all the way across the jaw, making both the upper and the cutting edges of the jaw clearly denticulate (noticeably toothed in outline).[7]

The alimentary canal of the digestive system forms two loops, as is true of all species within the family Arionidae.[20]


Geomalacus maculosus has a discontinuous or disjunct distribution. The slug is found only in Ireland (mostly the south west corner),[21] north-west Spain, and from central to northern Portugal.[22] It was once reported as occurring in France, but this has not been confirmed, so that record is considered suspect.[23] The presence of this slug in southwest Ireland might seem anomalous, but similar distribution patterns have been observed in other species of animals and plants. This particular disjunct distribution (in Iberia and Ireland without any intermediate localities) is known as a "Lusitanian".

There has been speculation that G. maculosus was introduced to Ireland from Iberia by prehistoric humans, as appears to have happened with the Eurasian pygmy shrew.[24][25] In support of such an origin, or of a more recent human-mediated introduction, the genetic diversity of the slug in Ireland was found to be greatly reduced compared with that in the Iberian populations.[26]


Within Ireland, G. maculosus is known from areas with sandstone geology in West Cork and County Kerry,[23] a total area of around 5,800 km2 (2,200 sq mi).[9] In 2010, a previously unknown population was recorded further north in County Galway.[21]

Protected sites[edit]

A significant proportion of the Kerry slug's range in Ireland is protected by being included in Special Areas of Conservation (SACs). In response to the European environmental legislation, Ireland has designated seven SACs with the slug named as a "selection feature":

In addition, St. Gobnet's Wood SAC (which was designated in relation to other selection criteria) was expanded in 2008 to protect Cascade Wood, a small area of woodland which is inhabited by the slug.[28]

The species has also been recorded at other SACs where it is not a selection feature, for example Derryclogher Bog in County Cork.[29]

Iberia: Spain and Portugal[edit]

Despite its first discovery at Caragh Lake, and its English common name of "Kerry slug", Ireland is at the periphery of this slug species' distribution; in terms of genetic diversity the distribution is centred on the north-western parts of the Iberian peninsula.[26][30] The species has been known from northern Spain since 1868, and from northern Portugal since 1873.[23]


The southernmost locality where this species is found is the mountain range Serra da Estrela in Portugal. Other Portuguese localities include the provinces Beira Alta, Douro Litoral, Minho, Trás-os-Montes e Alto Douro and the Peneda-Gerês National Park.[22][31]


The distribution of this species in Spain includes coastal locations in Galicia, and extends through the Cantabrian Mountains as far east as Mount Ganekogorta in the Basque Country. The localities fall within the boundaries of various autonomous communities: Galicia, Asturias, Cantabria, Castile and León (provinces of León, Palencia and Zamora), and the Basque Country (provinces of Biscay and Álava).[22][31] There have been unconfirmed findings of this slug from Navarra.[31]

Protected sites[edit]

Natura 2000 sites for this species in Spain include 48 localities (listed below, grouped by region). As at 2017, some of these sites have yet to be designated as Special Areas of Conservation:[27]

  • Asturias
Muniellos; PongaAmieva; Redes;
  • Cantabria
Camesa river; Liebana (Special Area of Conservation; Liébana (Special Protection Area); "Upper valleys of the Nansa and Saja and Alto Campoo");
  • Castile and León
Hoces de Vegacervera; Lake Sanabria and its vicinities; Montes Aquilanos (Site of Community Importance); Montes Aquilanos y Sierra de Teleno (SPA);
Natural Park of Fuentes Carrionas and Fuente Cobre-Montaña Palentina (SAC); Sierra de la Cabrera (SCI partially overlapping with a SPA of the same name).
  • Galicia
A Marronda; Anllóns river; Baixa Limia; Baixa Limia - Serra do Xurés; Baixo Miño; Bidueiral de Montederramo; Carballido, a yew wood in A Fonsagrada; Carnota - Monte Pindo; Cíes Islands; Costa Ártabra; Costa da Morte - two areas, Costa da Morte and Costa da Morte (Northern); Cruzul-Agüeira; Encoro de Abegondo-Cecebre; Eo river (included among the Galician sites although the estuary forms the boundary with Asturias); Costa de Ferrolterra-Valdoviño; Fragas do Eume; Macizo Central, Ourense (province); Monte Aloia; Monte Maior; Negueira; Pena Trevinca; Pena Veidosa; Serra do Candán; Serra do Cando; Serra do Xistral; Sil river canyon; Sobreirais do Arnego; Tambre - two areas, the river and its estuary; Támega river; Ulla-Deza river system
  • More than one region
Ancares - This district is divided between Galicia and Castile and León. Sierra de los Ancares is a mountain range which forms the boundary between the two autonomous communities, and which gives its name to a Natura 2000 site in the province of León.[32] On the Galician side of the sierra are two relevant sites - Ancares (protected under the Birds Directive) and Ancares-Courel (protected under the Habitats Directive).[33][34]
Picos de Europa - This mountain range is divided between three autonomous communities. The three sites listed (Picos de Europa, Picos de Europa (Asturias), Picos de Europa en Castilla y León) include protected areas in the Picos de Europa National Park and in a regional park in Castile and Leon that is also called Picos de Europa.


A brown and yellow spotted slug curled up into a tight ball so that its head is withdrawn completely, its mantle edge and tail are nearly touching, and none of its foot surface is exposed
The alarm response posture, which is found only in this species

This species of slug is primarily nocturnal, in other words it is usually only active at night. During the daylight hours, these slugs are usually hidden in crevices of rocks and under loose bark on trees.[35] In Iberia, juvenile slugs of this species become active during twilight, and adults become active at night, especially on rainy or very humid nights.[9][22][35] Ireland however is much further north, so the temperatures there are considerably cooler, there is more rain, and the air is often quite damp; in Ireland this slug is sometimes active in the daytime as long as the weather is humid and overcast.[17]

The Kerry slug has a defensive behavior that is very unusual in slugs. When attacked, most land slugs will simply retract the head and contract the body, but stay firmly attached to the substrate. In contrast, when this slug is threatened, it retracts its head, lets go of the substrate, rolls up completely, and stays contracted in a ball-like shape.[9] This is a unique feature among all the Arionidae,[10] and among all slugs in Ireland.[9]


A large dark green round patch of liverwort
The Kerry slug eats liverworts, probably including this species Pellia epiphylla, which is found in localities where the slug occurs in Ireland.[7]
Two slugs on the surface of a rock, which is dappled with various lichens including one spotted lichen not much larger than the slugs and somewhat similar in shape.
Two individuals among lichen patches on a rock are not easy to see because of their protective colouration.[7]


It was once thought that Geomalacus maculosus lives only in wild habitats.[23] However, in the Iberian Peninsula, although it does occur on tree trunks in oak (Quercus) and chestnut (Castanea) forest, it is easiest to find in synanthropic habitats such as rocky walls in oak or chestnut orchards, in ruins, near houses, churches and cemeteries.[36] In Ireland it also occurs in upland conifer plantations and areas of clear-fell.[37] Nevertheless, in neither part of its range is it an agricultural pest,[23] unlike some other slugs in the family Arionidae.

In Ireland, other habitats where it occurs are woodland with oak trees, oligotrophic open moorland, blanket bog and lake shores, especially if there are boulders covered with lichens and mosses in these habitats.[23][37] Although there was a geographical association with sandstone areas, the new locality in Galway is on granite.[37] In Iberia it usually occurs in granite mountains,[35] but also on slates, quartzite, schists, gneiss and serpentine.[38] The best predictor of its occurrence there is high rainfall and high summer temperatures.[36]


The food of Geomalacus maculosus includes lichens, liverworts, mosses, fungi (Fistulina hepatica)[17] and bacteria that grow on boulders and on tree trunks.[22][23][39]

In captivity, this species has been fed on porridge, bread, dandelion leaves, lichen Cladonia fimbriata and various vegetables: (carrot, cabbage, cucumber, lettuce).[9][7] It can be also carnivorous in captivity, and has been documented as devouring the snail Vitrina pellucida.[7]

Life cycle[edit]

A cluster of oval white eggs (22 are visible) on a leaf, looking rather like a miniature bunch of grapes.
A cluster of eggs deposited in captivity

The mating of this species is in head-to-head position with genital openings facing each other.[17] Atria are shaped as a funnel with fluted edges after mating.[17] As in Arion, sperm is transferred in a spermatophore.[40] Eggs are laid in July to October in the wild,[9] and from February to October in captivity.[39] Self-fertilisation is also possible in this species.[9] The eggs are laid in clusters of 18 to 30,[9] and held together by a film of mucus. The egg masses are about 3.5 × 2 cm in overall size.[39]

The eggs are very large compared with the size of the animal, but vary within certain limits. The largest eggs are more elongate, being 8.5 × 4.25 mm; the smallest eggs are more regularly oval, and are only 6 × 3 mm. All are semitranslucent milky-white or opalescent when fresh,[41] although some of the larger and more elongate ones show a somewhat transparent area at the smaller end. The opalescent (the color changes with the light direction like an opal) lustre becomes lost in a few days, and the eggs turn yellowish, and later brown,[7] or black.[39]

The young appear to hatch in from 6[39] to 8 weeks, at which period the spots on the body of the animal are barely present. However, the lateral bands are distinct and black, much more conspicuous than they are in mature slugs of this species. In juveniles the shield shows lyre-shaped markings, as is the case in slugs of the genus Arion. However these lyre-shaped markings become indistinct as the slugs grow larger. The slugs probably pass the winter in the sexually immature stage.[7] The body of preserved juvenile specimens is up to 3 cm (1.2 in) long with a mantle length of 10 mm.[9] Juveniles reach maturity in 2 years, at a length about 2.6 cm.[9][39] The life span of Geomalacus maculosus in the wild is up to seven years,[9] but the lifespan in captivity is rarely over three years.[39] In numerous different localities in Spain, it was consistently found to be the case that no more than a very few individuals of the species were observed at any one time.[35]

There were not known natural enemies of Geomalacus maculosus up to 2014.[42] Predators of Geomalacus maculosus include larvae of the third instar of the fly Tetanocera elata.[42]

Threats to the survival of the species[edit]

Flowering rhododendron bushes on one bank of a rocky stream surrounded by damp woodland habitat.
One threat to the habitat of this slug is the invasive plant species Rhododendron ponticum, as shown flowering here in Killarney National Park.

The most serious threat to the species is probably modification of the habitat, which reduces its lichen and moss food sources.[23] This can lead to the local disappearance of the species, which was documented in Spain.[23][35] Other threats include: intensification of land use (land reclamation, using of pesticides, overgrazing by sheep, removing of shrubs, building gardens, burning, and building roads and highways), tourism, general development pressure, coniferous forest plantations, the spread of invasive species of plants such as Rhododendron ponticum and habitat fragmentation[23][43] (see also Moorkens 2006).

Other potential dangers to the species include climate change and air pollution, because these negatively affect the lichens which are a food source for the slug. Climate change will probably affect the Iberian populations more seriously, because the climate there is already on the hot and dry side relative to Ireland, which is generally rather cool and damp.[23]

Conservation measures[edit]

International protection[edit]

Because of its perceived rarity and its restricted distribution, Geomalacus maculosus is protected under the Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention), EIS Bern Invertebrates Project. This decision was backed by studies of its distribution and ecology in Ireland[17] which concluded that evidence of a decline in Iberia, plus uncertainty over its status in Ireland, tended to support its inclusion in the Convention. Since 2006, Geomalacus maculosus has been considered a least concern species in the IUCN Red List,[1] however, during 1994 to 2006 the slug was rated as vulnerable.[23]

Geomalacus maculosus is also protected by the European Union's Habitats Directive (which was a response to the Bern Convention) and has been listed as an Annex II and Annex IV species since 1992.[44] There are two principal mechanisms used by the Directive to protect habitats and species:

Seven SACs have been designated for this species in Ireland and 49 SCIs in Spain.[27] It is probably in areas not specifically protected as SACs that threats to the Kerry slug will be greatest. The Habitats Directive protects the Kerry slug outside the SACs by Article 12 (1), which obliges European Union member states to:

  • establish ‘a system of strict protection’ for listed species
  • prohibit deliberate capture or killing
  • prohibit ‘deliberate disturbance … particularly during the period of breeding, rearing, hibernation and migration’
  • prohibit ‘deliberate destruction or taking of eggs from the wild’
  • prohibit the deliberate or non-deliberate ‘deterioration or destruction of breeding sites or resting places’.

Protection in Iberia[edit]

Conservation status reports from Portugal and from Spain were not yet available in August 2009.[45]

Its conservation status in Spain for the IUCN criteria is vulnerable.[31]

Protection in Ireland[edit]

In 1988 Platts and Speight noted that only three of the Irish sites where the slug occurred were protected: Glengariff Forest, West Cork; Uragh Wood Nature Reserve, South Kerry; and Killarney National Park, North Kerry. They concluded that the species could not be adequately safeguarded with only three sites, and therefore they supported its inclusion in the Bern list, to which the Irish government is a signatory.[17]

The Habitats Directive was transposed into Irish law by:

  • The EC (Natural Habitats) Regulations 1997.[46] This was the principal legislation transposing the Habitats Directive and upgraded the protection of the Kerry slug's habitat by the designation of Special Areas of Conservation (as listed in the distribution section above).
  • Adapting existing legislation. The Kerry slug has been protected since 1990 under the Irish Wildlife Act of 1976; it was added to the list of protected species by Statutory Instrument 112/1990, and was the only gastropod so protected.[44][47] The treatment of the Kerry Slug has been cited in the media as an example of hyperprotectionism (specifically, in the context of delays in the construction of a proposed by-pass in County Cork).[48] However, The Wildlife Act does not protect the slug from authorised or unauthorised indirect damage, but only from wilful direct damage such as collecting.

The Irish National Parks and Wildlife Service published a Species Action Plan for the Kerry slug in January 2008.[23][49] Efforts were made to protect the slug from indirect damage arising, for example, from commercial forestry.[50] However, following a legal challenge to Ireland's transposition and implementation of the Habitats Directive, the Action Plan was superseded in May 2010 by a Threat Response Plan. The Threat Response Plan addressed issues which arose when the European Court of Justice held that Ireland was not protecting the Kerry slug with the strictness that the directive required in respect of a species listed in annex 4.[29][51]


In a report to the European Commission covering 1988–2007, the conservation status of the species in Ireland was declared "favourable (FV)" in all evaluated criteria (range, population, habitat and future prospects).[9][43] However, the validity of this assessment was put into question by the European Court of Justice ruling discussed above, which held that Ireland was not monitoring the slug properly.[24]

The need to improve monitoring was discussed by the NPWS Threat Response Plan of 2010, which recognised that population statistics were still deficient, particularly outside the SACs. As the Threat Response Plan noted, species monitoring is a process in which distribution and status of the subject are evaluated systematically over time. Under this definition no monitoring of the Kerry Slug had yet been undertaken in Ireland as of May 2010.[29] In order to take matters forward, the Kerry Slug Survey of Ireland, a collaboration between the National Parks and Wildlife Service and the Applied Ecology Unit at the National University of Ireland, Galway, researched a "suitable monitoring protocol" for the species.[28][52] The Kerry Slug Survey's investigations resulted in the publication of a guide to the population dynamics of the Kerry slug; this guide was published as part of the Irish Wildlife Manual series in 2011.[53]

Captive breeding[edit]

Since 1990, the species has been successfully bred in captivity. The Wildfowl & Wetlands Trust, a British conservation organisation, operates a captive breeding programme in terraria at its "Endangered Species Breeding Unit". The project is located not within the species' normal range, but in England at the Martin Mere Wetland Centre.[39] During the 1990s, slugs from the breeding programme were given out to a number of different zoos and individuals in order to set up their own breeding programmes, but unfortunately only a very few of those breeding groups survived.[39]


This article incorporates public domain text from Taylor (1907).[7]

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  53. ^ Mc Donnell, R.J. and Gormley M.J. (2011). Distribution and population dynamics of the Kerry Slug, Irish Wildlife Manual No 54, National Parks and Wildlife Service, Department of Arts, Heritage and the Gaeltacht, Dublin

Further reading[edit]

External links[edit]