common name: terrestrial slugs of Florida
scientific name: Gastropoda: Stylommatophora

Introduction - Biology - Economic Importance - Management - Identification of Slugs Found in Florida - Key to the Families - Florida Species by Family - Selected References

Introduction

Biology

Fig. 1. breathing pore

Most slugs are hermaphroditic, possessing both male and female sex organs. Thus, at least in some species, a single individual can inseminate another slug, can be inseminated by another, and can even inseminate itself! This makes slugs particularly dangerous as invaders, because even a single individual that escapes detection can establish a population in a new environment through self-fertilization. Eggs are white or translucent and often nearly spherical. They usually are laid in clusters either in the soil or similar locations that conserve moisture, and may be interspersed with mucus secretions. Eggs are not very resistant to desiccation, so they must remain in fairly humid environments if hatching is to be successful. Some slugs deposit fecal-like material with their eggs, but the reason for this behavior is unknown. Development time of slugs varies with weather conditions and among species, but several months or more are commonly required for slugs to reach maturity. Slugs often develop faster and commence reproduction sooner under warm conditions, but attain a larger size and ultimately produce the same number or more eggs at cooler conditions.

Fig. 2. eggs

Slugs tend to have omnivorous dietary habits. Many feed on fungi, decomposing vegetation, and soil as well as living plant tissue. They are opportunistic, so their dietary often reflects what is available as well as innate and learned preferences. Some slugs thrive in disturbed habitats linked to human activity (anthropogenic), establishing the potential to become pests of agricultural or ornamental plants. Their nocturnal habits and ability to burrow into the soil make them difficult to detect. Their mouth contains a rasping structure called a radula, which bears tooth-like features, but these are internal and not generally visible. Young slugs may feed only on the surface of vegetation but larger slugs remove entire sections of foliage, leaving irregular holes in foliage, flowers, and other soft plant tissue.

Fig. 3. foliar damage

Fig. 4. foliar damage

Slugs can be quite long-lived, surviving for a year or more. Unlike some invertebrates such as insects, they can continue to grow after they reach reproductive maturity and commence egg production. Thus, their adult size range is quite variable. Their eggs are not all produced in a single batch; instead, they are deposited periodically in soil or leaf litter.

Economic Importance

One slug species that has successfully invaded Florida, Sarasinula plebeia (P. Fischer, 1868), is a serious pest in Central America. Sarasinula plebeia likely reached Florida from South America via Central America. Rueda et al. (2002) estimated that this slug causes between $27 million and $45 million damage to dry bean crops annually in Central America. Slugs damage and often kill the germinating beans, a major source of protein for the farmers. However, agricultural practices and probably other factors have apparently resulted in no crop damage in Florida by S. plebeia. Although Cowie et al. (2009) rated S. plebeia as a high-risk gastropod to the United States, it has not yet proved to be a problem in Florida.

A slug that commonly causes damage in Florida is Deroceras laeve (Müller, 1774). This small species apparently is indigenous, or at least is widespread, in North America. Deroceras laeve become most active and damaging during the cooler, wet conditions of spring and early summer and do not cause much foliage damage during the hotter months of summer even when moisture is abundant. Damage by D. laeve often goes undiagnosed because like all slugs, they feed only at night. Heavily mulched planting beds provide excellent harborage for this slug, including shelter during the daylight hours. Flower and foliage plants suffer the most damage in Florida, but this slug attacks many different plants. Leidyula floridana (Leidy, 1851) also inflicts injury to plants though this species usually it is not abundant.

Although not usually considered to be important pests in Florida, elsewhere in the USA some of the introduced European slugs have caused great damage on many vegetable, field crop, and ornamental plants. Some may transmit plant disease-causing organisms such as viruses and fungi, or serve as intermediate hosts of animal parasites such as tapeworms and lung worms (Godan 1983). The tropical veronicellids also are a threat to animals and people because they serve as intermediate hosts of the nematode Angiostrongylus costaricensis, which causes a disease called human abdominal angiostrongyliasis (Rueda et al. 2004). Although outbreaks of this rodent-associated disease occur in Central America, it occurs infrequently in the United States.

Several potentially damaging slugs have been intercepted in commerce but apparently failed to establish in Florida. These include:

• black arion, Arion ater (Linnaeus, 1758)
• brownbanded arion, Arion circumscriptus Johnston, 1828
• gray field slug, Deroceras reticulatum (Müller, 1774)
• yellow garden slug, Limacus flavus (Linnaeus, 1758)
• giant garden slug, Limax maximus (Linnaeus, 1758)
• greenhouse slug, Milax gagates (Draparnaud, 1801)

Management

Slug control and management have been reviewed by many authors (e.g., Henderson and Triebskorn 2002, Bailey 2002). The management tools for slugs are much the same as used in the integrated pest management (IPM) strategies for other invertebrate pests such as insects. However, development of chemicals and research on biological control (i.e., potential predators and parasites) have been done mostly outside of the USA, and options are more limited than with insects.

A comprehensive review of the natural enemies of terrestrial slugs can be found in Barker (2004). Natural enemies are relatively few. Some birds, especially ducks, feed on slugs. Moles and shrews also will feed on slugs. Few predaceous insects attack slugs, but in Coleoptera the larvae of Lampyridae (lightningbugs) and adult Carabidae (ground beetles) do so occasionally. Some parasitic flies (Diptera, especially marsh flies, family Sciomyzidae and phorid flies, family Phoridae) a few fungi, and many protozoa are known to affect slugs (Godan 1983). Phasmarhabditis hermaphrodita, a slug-parasitic nematode, is used in Europe to control slugs but is not allowed in the USA. Other nematodes found in the USA have been investigated for slug control, but the results were not encouraging.

Predatory snails such as the rosy wolf snail, Euglandina rosea (Férussac, 1821), will attack slugs, and may account, in part, for the relatively low slug densities in Florida. Euglandina rosea prefers snails to slugs, but will attack and consume small slugs in the absence of snail prey. Euglandina rosea is native to the southeastern USA, and is quite common in woodlands and gardens in Florida. It has been relocated to other parts of the world, including Hawaii, India and many islands in the Pacific region, in an attempt to control invasive snails such as giant African land snail, Achatina fulica (Férussac, 1821). It has been used to provide partial control of giant African snail, but it has been quite disruptive to native snail populations, so its use is discouraged outside its natural range (Barker 2004).

Fig. 5. E. rosea

Slugs benefit from having shelter such as plant debris, so removal of boards, rubbish, piles of brush, and other debris will help limit slug numbers. On the other hand, strategic placement of such shelter can be used to sample or even reduce slug populations if the slugs are removed and destroyed periodically.

Moisture is also an important factor governing slug distribution and activity. Dense vegetation, deep mulch, and frequent irrigation favor slugs. Consequently, minimizing irrigation (especially overhead sprinkling) or planting drought tolerant vegetation may reduce slug problems.

When chemical control is needed, commercial slug and snail baits are usually used by scattering bait around vegetation that is to be protected. The bait contains a toxicant, of course. Traditionally, the toxicant in such baits is metaldehyde, or sometimes metaldehyde plus a carbamate toxicant, or occasionally a carbamate toxicant alone. These are effective, but quite toxic, and they pose a threat to non-target organisms such as pets and vertebrate wildlife. More recently, iron phosphate (normally considered to be a plant fertilizer) has been shown to be an effective toxicant when applied to slug and snail baits, and is much safer to use. Regardless of the toxicant, baits should be scattered thinly in and around vegetation, so as to make it unlikely that pets or wildlife will ingest too much of the bait. If possible, it is a good idea to irrigate prior to bait application, because the additional moisture will stimulate increased slug activity, increasing the likelihood that they will eat the bait. Poisoned slugs typically display loss of coordination and paralysis, and increased mucus secretion. They often die from desiccation following paralysis, but detoxification of the poison by the slug is sometimes accomplished, so they may recover and survive (Henderson and Triebskorn 2002).

Identification of Slugs Found in Florida

Fig. 6. Diagram of extended (above) and contracted (below) slugs, with key morphological features labeled.

Key to the Families

1. Mantle covering all of the back (dorsum) of the animal, or nearly so, or saddle-like mantle structure not apparent in anterior region when body is extended (Figs. 15–18); breathing pore (pneumostome) not visible or located anteriorly (toward the head) on right margin of mantle (although it may be closed) (Fig. 7) . . . . . . 2
1'. Mantle consisting of an elevated saddle-like structure that is apparent when the body is extended, and located only in the anterior region of the body (Figs. 19–23); breathing pore (pneumostome) present (although it may be closed) posteriorly (away from the head) on right margin of mantle (Fig. 7) . . . . . . 3

Fig. 7. Diagram of slugs, showing two types of mantles, and alternate positions of the breathing pore
(the arrow points to pore) relative to mid-point of mantle. Slugs at top (a,b) have the mantle located only
anteriorly. This is often called a 'saddle-like' mantle. Slug 'a' shows anterior (relative to the mid-point)
location of pore; slug 'b' shows posterior location. The slug shown below (c) has the mantle covering 2/3
of its body, but the anterior (head) region is exposed. Several slugs found in Florida have yet another
mantle arrangement, wherein the entire dorsal surface is covered with the mantle.

2(1). Body circular or oval in cross-section, and not tapering laterally (toward the sides) (Fig. 10); breathing pore (pneumostome) found near anterior right mantle edge; foot nearly as wide as body (Fig. 11) - Family Philomycidae, the mantleslugs
2'. Body rather flattened in cross-section, and tapering laterally (toward the sides); breathing pore (pneumostome) not visible (Figs. 15–18); foot considerably narrower than width of body (Figs. 8, 9) - Family Veronicellidae, the leatherleaf slugs

Fig. 8. View of veronicellid slugs showing diagnostic features visible from below (ventrally). Drawing
on left (a) illustrates genital pore not adjacent to foot, near center of hyponotum; drawing in center (b)
shows genital pore adjacent to foot, at the edge of the hyponotum; and drawing on right (c) shows tip
of foot being lifted to expose anal slit.

Fig. 9. ventral surface of slug

3(1'). Ridges on mantle forming fingerprint-like pattern that is not centered dorsally, rather being offset slightly to the right side of the animal - Family Agrolimacidae
3'. Ridges on mantle forming fingerprint-like pattern that is centered dorsally (Figs. 22, 23) - Family Limacidae, the keelback slugs

Florida Species by Family

This large slug has its mantle extending the entire length of its body. It can be 3–10 cm long at maturity. Typically, it is tan with brown or black spots and blotches. In addition, there may be two rows of dark spots along the back (dorsum) (Fig. 10). However, this slug can be somewhat variable in appearance, and sometimes is fairly pale or mostly dark. The foot is nearly as wide as the body (Fig. 11). The breathing pore (pneumostome) is located in a lightly pigmented anterior right area of mantle (Figs. 12, 13). This slug can grow to weigh 8 g, though it becomes sexually mature and begins egg production when it is about 3 g. This species feeds preferentially on fungi, but will also consume live vegetation. It is commonly found under logs, loose bark, and aerial bromeliads. This species normally is found in woodlands, and does not frequent disturbed habitats like the veronicellid slugs. The Carolina mantleslug is a native species, found from Maine to Florida, and west to Iowa and Texas. Named subspecies exist, and it may be comprised of a species complex.

Fig. 10. Carolina mantleslug

Fig. 11. ventral view of Philomycus

Fig. 12. lateral view of Carolina mantleslug

Fig. 13. breathing pore of Carolina mantleslug

An entirely albino or tan-colored form of Carolina mantleslug occurs in southernmost Florida, where it lives under loose bark and feeds on fungi growing on partly submerged trunks of dead hardwood trees. Like the more common forms, it is a large slug, attaining up to 8 g in weight and 10 cm in length.

Fig. 14. albino Carolina mantleslug

This is a very small slug, less than 1 cm long. Its mantle covers only the posterior 2/3 of the animal and is thicker in the anterior region of the mantle, giving the slug a hump-backed appearance. (Fig. 7c). Its background color is whitish or tan, but it bears numerous black spots. The spots sometimes coalesce to form blotches, and may also form an interrupted irregular line laterally on the mantle. This slug occurs widely in the eastern USA, but in Florida it is documented only from Marion County. Due to its small size and preferred habitat (deciduous woodlands) it may well be more broadly distributed, but overlooked. In Illinois, it is reported to occur under loose bark, often in association with Philomycus carolinianus.

The related but larger Megapallifera mutabilis (Hubricht, 1951), also known as the changeable mantleslug, is known from counties in Alabama adjacent to Florida and may occur in the Panhandle region of Florida but so far is unreported there.

Pallifera fosteri has also been known as P. fosteri oughtoni (Webb 1952).

Family Veronicellidae, the leatherleaf slugs

Adults of this species are uniformly black in color dorsally, and velvety in appearance (Fig. 15), with the underside paler in color. The velvety black color of these slugs occasionally is interrupted by a pale median stripe, especially in juveniles. The very young slugs are not so darkly colored. Because of this black velvety appearance, it is unlikely to be confused with any other slug found in Florida. It can attain a length of 5 cm when extended, but is not a large slug, attaining a weight of about 1.2 g at maturity. Like most slugs, B. angustipes is usually seen only during wet weather, spending most of its life foraging at night in leaf litter or in the soil. A native of South America, this species is now established in the states that border the Gulf of Mexico (Walls 2009), including northern and central Florida. It occurs in greenhouses and nurseries, where it can be found under potted plants, so it is destined to be spread further with nursery stock. The slug also burrows in soft soil and can enter the root-balls of plants through drainage holes at the base of the containers. This species reportedly eats both living and decayed leaves, although it is not considered to be a pest in Florida because it is not abundant. Sometimes it is found in lawns (Walls 2009) and disturbed areas near homes, such as drainage ditches. Most slugs, including B. angustipes, can be involved in the life cycle of disease-causing parasites, and although this is a concern in the tropics, there is no evidence of a problem in Florida.

Early references refer to this species either as Angustipes ameghini (Gambetta, 1923) or Veronicella ameghini Gambetta, 1923.

Fig. 15. black-velvet leatherleaf

This slug is tan dorsally, and mottled with brown or black spots that often coalesce into dark dorsolateral stripes (Fig. 16, 17), and bearing a long, pale medial stripe. The genital pore is located adjacent to the foot (Fig. 8), normally less than 1/4 hyponotal width (the hyponotum is the portion of the mantle that wraps beneath the slug body and is adjacent to the foot) from the foot. The anal slit (Fig. 12) usually is visible, extending beyond the right edge of the retracted foot. It is native to the Caribbean (Cuba to Jamaica) and southern Florida. Formerly found only in southern and central Florida, it has since has spread to northernmost Florida, and also is found in Louisiana, Texas, and northeastern Mexico, suggesting either that the species is more widespread than previous records indicated or that it is being relocated via commerce. Normally, it is the most commonly encountered veronicellid in Florida. No serious economic damage has been reported thus far from Florida although they feed readily on both crop and ornamental plants. These slugs can attain a weight of 12 grams and measure over 5 cm in length.

Leidyula floridana has also been known as Vaginulus floridanus (Tate, 1870) and Veronicella floridana (Leidy, 1851).

Fig. 16. Florida leatherleaf - contracted

Fig. 17. Florida leatherleaf - extended

This slug is light to dark brown dorsally, often with a dark medial stripe (Fig. 18). It is native to South America but has spread to Central America and Mexico, where it has become a serious pest of beans in intercropped corn-bean farming systems, and it affects other horticultural crops as well, including tomatoes and peppers, and some ornamental plants (Rueda 1989). Although having broad dietary habits, dicots are preferred over monocots. Sarasinula plebeia superficially resembles the native L. floridana, but normally can be distinguished by the position of the female genital pore (more than 1/4 hyponotal width from foot) and by the usual absence of the dorsomedial light stripe found in L. floridana. In Florida, this species is normally found only in southern Florida, though there are reports of it occurring in central Florida as well. This is a large slug, attaining a weight of 4–15 g. It has a high rate of reproduction; Rueda (1989) reports an average of four egg clutches containing about 30 eggs for total egg production of about 120 eggs per slug. He also reported a pre-reproductive period of 80 days and a life span exceeding 200 days.

In Florida, initially this species was misidentified as Leidyula moreleti, but L. moreleti is not known from Florida. It has also been known as Vaginulus plebeius P. Fisher, 1868; Vaginula plebeja P. Fisher 1868; Sarasinula plebeja Grimpe & Hoffman, 1925, and others.

Fig. 18. Caribbean leatherleaf

Other veronicellids have been found in Florida, or may soon become established. One is Veronicella sloanei (Cuvier, 1817) also known as the pancake slug. The pancake slug is large, often 5–12 cm in length, and usually very pale, ranging from whitish to tan or speckled with brown spots. Especially in juveniles, their body may bear two dorsolateral stripes extending from behind the antennae backward along the body, though they are rather diffuse. The eyestalks are bluish. In Florida, this species has been observed only in Miami-Dade County, and it is uncertain whether it persists. Elsewhere, pancake slug is found throughout the Caribbean, and some islands in the Pacific, including Hawaii. It has a very wide host range, including many vegetables and ornamental plants.

Also threatening is Veronicella cubensis (L. Pfeiffer, 1840), known as the Cuban slug. This slug is 5–12 cm long, and variable in color but usually brown with dark but thin dorsolateral stripes along it back, and a thin light-colored stripe dorsally. It is very difficult to distinguish from some of the slugs already established in Florida. Like the pancake slug, it occurs widely in the Caribbean and the Pacific, where it feeds on numerous crop and ornamental plants. It has been intercepted in Florida and apparently is established in Santa Barbara County, California.

Family Agrolimacidae

This is the smallest of the common slugs in Florida, weighing only as little as 0.2 g at maturity, but up to 0.8 g. It is brownish or grayish, without spots or stripes, and bears only indistinct markings, often including minute white flecks (Figs. 19, 20). Though only 1 cm long at rest, the marsh slug can become more elongate (up to 3 cm) when extended. The eggs are deposited in small clusters (often six to 10, but up to 33) in soil or organic detritus. The eggs initially are transparent but become yellowish as they mature, usually hatching in twop to three weeks (Faberi et al. 2006). They are 1–3 mm long, and vary from round to oval in shape. This species is found widely in North America but also occurs in Europe, Asia, and South America. In Florida, it is found from the Keys to Pensacola, and feeds on a great number of plants in cultivated areas as well as in swamps, woodlands, and around human habitations. Although tolerant of a wide range of environmental conditions, in Florida it is inactive during the heat of the summer. Its temperature tolerances appear to be broader than that of the gray field slug, Deroceras reticulatum (Getz, 1959), a much more damaging species in North America. This attribute likely explains the presence of marsh slug in Florida but the absence of gray field slug.

Although formerly a bit confused, the scientific name and identity of D. laeve have been stable for many years.

Fig. 19. marsh slug - grayish morph

Fig. 20. marsh slug - brownish morph

Family Limacidae, the keelback slugs

This slug (also known as threeband garden slug) is larger than Deroceras laeve, attaining a length of 5–7 cm, although it begins reproduction when considerably smaller, about 2.5 cm long and 1.2 g in weight. It is light brown or reddish brown with a pair of dark dorsolateral stripes extending over the mantle and body (Figs. 21–23). Despite the name 'keelback' being applied to this family, this species shows little or no evidence of a keel (dorsal ridge on the tail). Originally from southwestern Europe, it has been introduced to many states in the USA from New York to California and Hawaii, but in northern areas it is found mostly in greenhouses (Skujiené 2002). It deposits clusters containing up to 63 eggs that hatch in about 14 days. They measure 2.0–2.5 mm in length and are oval in shape. Like other problem slugs, it is anthropogenic, and often found near human habitations. In Florida, it is established only in the Pensacola area. It has also been introduced to many other countries, including Australia, New Zealand, some Pacific islands, and regions of South America.

The name of this species has changed repeatedly (e.g., Limax valentianus [Férrusac, 1823], Limax poirieri [Mabille, 1883]), and most North American records for this species refer to it as Lehmannia marginata (Hoffman, 1928)

Fig. 21. banded slug

Fig. 22. banded slug

Fig. 23. banded slug

Selected References

• Auffenburg K, Stange LA. (August 2008). Snail eating snails of Florida (Euglandina rosea (Férrusac 1821), Rumina decollata (Linnaeus 1758), Haplotrema concavum (Say 1821), Gulella bicolor (Hutton 1834), Varicella gracillima floridana Pilsbry 1907). Featured Creatures. http://entnemdept.ifas.ufl.edu/creatures/misc/gastro/snail_eating_snails.htm (1 June 2011).
• Bailey SER. 2002. Molluscicidal baits for control of terrestrial gastropods. Pages 33-54 in Barker GM. (ed.) Molluscs as Crop Pests. CABI Publishing, Wallingford, UK.
• Barker GM. (ed.) 2001. The Biology of Terrestrial Molluscs. CABI Publishing, Wallingford, UK. 558 pp.
• Barker GM (ed.) 2002. Molluscs as Crop Pests. CABI Publishing, Wallingford, UK. 468 pp.
• Barker GM (ed.) 2004. Natural Enemies of Terrestrial Molluscs. CABI Publishing, Wallingford, UK. 644 pp.
• Cowie RH, Dillon Jr RT, Robinson DG, Smith JW. 2009. Alien non-marine snails and slugs of priority quarantine importance in the United States: a preliminary risk assessment. American Malacological Bulletin 27: 113-132.
• Deisler JE, Stange LA. 1984. The verocellid slugs of Florida (Gastropoda: Veronicellidae) Florida Department of Agriculture and Consumer Services Entomology Circular 261. 4 pp.
• Faberi AJ, López AN, Manetti PL, Clemente NL, Álvarez Castillo HA. 2006. Spanish Journal of Agricultural Research 4: 345-350.
• Garcia EN, Thomé JW, Castillejo J. 2007. A review of the Veronicellidae from Mexico (Gastropoda: Soleolifera). Revista Mexicana de Biodiversidad 78: 41-50.
• Getz LL. 1959. Notes on the ecology of slugs: Arion circumscriptus, Deroceras reticulatum, and D. laeve. American Midland Naturalist 61: 485-498.
• Henderson I, Triebskorn R. 2002. Chemical control of terrestrial gastropods. Pages 1-31 in Baker, G.M. (ed.) Molluscs as Crop Pests. CABI Publishing, Wallingford, UK.
• Jacksonville Shell Club. Northeast Florida slug page. www.jackshells.org. http://www.jaxshells.org/807b.htm (1 June 2011).
• Karlin EJ, Bacon C. 1961. Mating, and egg-laying behavior in the Limacidae (Mollusca). Transactions of the American Microscopical Society 80: 399-406.
• Rueda A. 1989. Biology, Nutritional Ecology, and Natural Enemies of the Slug Sarasinula plebeia (Fischer, 1868) (Soleolifera: Veronicellidae). Unpublished M.S. Thesis, University of Florida, Gainesville. 163 pp.
• Rueda A, Caballero R, Kaminsky R, Andrews KL. 2004. Vaginulidae in Central America, with emphasis on the bean slug Sarasinula plebeia (Fischer). Pages 115-144 in Barker, G.M. (ed.) Molluscs as Crop Pests. CABI Publishing, Wallingford, UK. 468 pp.
• Robinson DG. 1999. Alien invasions: the effects of the global economy on non-marine gastropod introductions into the United States. Malacologia 41: 413-438.
• South A. 1992. Terrestrial Slugs: Biology, Ecology and Control. Chapman and Hall, London. 428 pp.
• Skujiené G. 2002. Lehmania valentiana (Férussac, 1823)- a newly introduced slug species in Lithuania (Gastropoda: Pulmonata: Limacidae). Act Zoologica Lituanica 12: 341-344.
• Walls JG. 2009. Just a plain black slug: Belocaulus angustipes. American Conchologist 37: 28-29.

Authors: John L. Capinera, Jodi White, University of Florida; and Gary Bernon, USDA-APHIS
Photographs: Lyle J. Buss and John Capinera, University of Florida; and William Leonard
Graphics: Kay Weigel, University of Florida
Project Coordinator: Thomas R. Fasulo, University of Florida
Publication Number: EENY-494
Publication Date: June 2011. Latest revision: November 2011.
Copyright 2011 University of Florida

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