Group H Key
The data bases include 17 species from 6 general and 4 families. The list includes both 9 native and 8 exotic species. A few species were found very rarely and might be misidentified.
In "nature", slugs can be found in woodlands and meadows, usually under something (leaves, branches, and so on), but also crawling on surfaces, especially after rains. Limax and urban slugs likes wet areas, including garages, basements, and trash or waste piles. Much maligned and not well-regarded by gardeners, slugs live by their wits - or rather their protective slime and habitat preferences.
The image below shows two Giant Garden slugs (Limax) on the siding of a house getting ready to mate.
The important characters used in identifying slugs are:
1. the extent to which the mantle covers the body (almost entirely - or - partially at the anterior end)
2. the placement of the breathing pore or pneumostome (anterior half of mantle - or - posterior half)
3. presence or absence of a keel at the posterior
4. grooves or other surface features
5. color of slime
6. body length (when extended)
A good resource for information on slugs found in the region (and a key for the exotic species) is the Field Guide to the Slugs of Kentucky (will open as a pdf). Dourson's Land Snails of West Virginia (2015) is also very good and has the native Philomycids.
All of the slug maps below should be considered to be "speculative". The records for slugs, since they need a live animal, are probably under-represented. All the slugs are probably more common than indicated, especially the exotics that favor human habitations. Interesting, it appears that slugs appear more often in iNaturalist posts compared to shelled gastropods, than they are a proportion of the gastropod fauna.
Key to Families of Slugs modified from Oesch et al. 2013
1a. Mantle very large, covering more than 2/3 of body – go to Philomycidae
1b. Mantle smaller, covers less than ½ or so of body – go to 2
2a. Breathing pore located in front half of the mantle – go to Arionidae
2b. Breathing pore located in back half of the mantle – go to 3
3a. Color usually uniform, light cream to dark gray or black, rarely with pigmented blotches or reticulations on the body outlined in dark colors; size smaller, length less than 50 mm extended – go to Agriolimacidae
3b. Color patterned with bold dark blotches or faint to dark stripes; size larger, usually 60 mm or more extended - go to Limacidae
The keys below are an amalgam of information from the two sources given above plus Oesch (2013). Since no one source describes all the species or even gives a specific key, the attempt at a key here is tentative and identifications should consider the descriptive information in the sources. I'm just trying to narrow it down. If you need a closer look to see characters, you can often tease them onto twigs for a better look without actually touching them.
Arion slugs are a group of invasive species of European origin. Some can damage agricultural crops and ornamental plants, while some are garden pests. They can compete with native slugs.Very few (as you will see by the maps below) were listed in the databases. In fact, Nature Serve only notes Arion fasciatus as being in Indiana. But invasives (or exotics) could be around. It is safe to say that the actual species present and their general locations are not known. It is possible that some species of Arion not listed here might be present as well. This is a start, anyway. The Indiana map shows any occurrence of an Arion slug in the databases.
Key to the species of Arion - modified from KY and MO keys (also see images and descriptions - including habitats - at Hotopp et al. 2013):
1a. Very small slug (< 2.5 cm); a spiny appearance when contracted (needs a hand lens); head and tentacles noticeably darker than rest of the body - Arion intermedius (MO WV)
1b. Larger slug; does not look spiny when contracted – go to 2
2a Slug contracts into a hemispherical shape when disturbed; body mucus colorless; sole grayish white; up to 5 cm in length - Arion fasciatus (KY WV)
2b Slug does not contract into a hemispherical shape when disturbed; body mucus orange-yellow; foot sole pale yellow and sometimes translucent in appearance; up to 7 cm in length, probably the most common species - Arion subfuscus (MO KY WV)
Arion circumscriptus is not included due to lack of information.
Brown-banded Arion Slug
Arion circumscriptus Johnston, 1828
Orange-banded Arion Slug
Arion fasciatus (Nilsson, 1823)
Hedgehog Arion Slug
Arion intermedius (Normand, 1852)
Dusky Arion Slug
Arion subfuscus (Draparnaud, 1805)
Two species from this family have been recorded - the Meadow Slug and the Gray Fieldslug. The Meadow Slug may be found in grasslands and woodlands, but also residential lawns, gardens and greenhouses. Its classification is compound - it is thought to be native in some parts of the USA, but may be invasive in others. On the other hand, the Gray Fieldslug is an exotic species which can be found in gardens and fields, and is an agricultural pest.
Key to the species of Deroceras - modified from KY and MO keys (also see images and descriptions - including habitats - at Hotopp et al. 2013):
1a. Border of the breathing pore is darkly colored; size 15 to 30 mm; nucleus on the mantle is located at the left posterior side; slime is clear and watery - Derocerus laeve (MO KY WV)
1b. Border of the breathing pore is white; size 35 to 50 mm; nucleus on mantle is on the right of the midline; slime when animal is irritated is milky colored and viscous - Deroceras reticulatum (MO KY WV)
Deroceras laeve (Muller, 1774)
Deroceras reticulatum (Muller, 1774)
These slugs from the family Limacidae are invasive species of European origin. These will be found around houses (or in basements), gardens, parks, and so on, associated with damp human structures. Their size (length and bulk) is an obvious identifier. The image shows the typical aerial mating of the Giant Garden Slug, hanging from the siding of a house. Their distribution in the state, especially Limax, is wider than shown (as indicated by iNaturalist posts).
Key to the species of Limacidae - modified from KY and MO keys (also see images and descriptions - including habitats - at Hotopp et al. 2013):
1a. Body yellowish with distinct green mottling; tentacles contrasting oily blue; mucus slippery and plentiful; keel often marked by a pale yellow line (sometimes only obvious near the tip of the tail); mucus yellow; up to 120 cm in length - Limacus flavus (KY WV)
1b. Mantle spotted or marbled black; tentacles light to dark brown; mucus colorless, sticky and sparse; keel obvious; lateral bands may be present on the tail but are always absent from the mantle; up to 200 mm in length - Limax maximus (KY WV)
The aerial mating of the Giant Garden Slug, hanging from the siding of a house.
Limax flavus Linnaeus, 1758
Giant Garden Slug
Limax maximus Linnaeus, 1758
Mantle Slugs are a group of native species of slugs where the mantle most all (at least 2/3) of the body. They are comprised of three genera: Megapallifera, Pallifera, and Philomycus. Find them in woodlands, under and around bark, likeing damp areas. On the trail, look alongside on woody debris.
Key to the species of Philomycidae - modified from WV and MO keys (also see images and descriptions - including habitats - at Hotopp et al. 2013):
Key to the species of Philomycidae modified from Oesch et al. 2013 and Dourson 2015. There is in this key, as in a couple of others, more than a little "by gosh and by golly" as no source treats all the species together and the descriptions do not always allow for a direct trait-by-trait comparison. Two species are not included in the key: Pallifera hemphilli and P. megaphallica - their presence is uncertain. So, use sources to evaluate where the key takes you. It is a start.
1a. Length 75-100 mm extended; mantle extends to cover the entire head; color gray to brown with two rows of elongated black spots on either side of the dorsal midline – go to 3
1b. Length usually less than 80 mm extended; mantle does not extend to cover entire head; color variable, but without dorsal rows of elongated spots - 3
2a. Larger in size, dark rows of black spots on either side of the dorsal midline - Philomycus carolinianus (MO WV)
2b. May be smaller (50-100 mm extended), without or with pale black spots on either side of the dorsal midline - Philomycus flexuolaris (WV)
3a. More of a stouter body; length 80 mm or less when extended; mantle not does not cover entire head - Megapallifera mutabilis (MO WV)
3b. More of a slender body; length 50 mm or less when extended; mantle not does not cover head – go to 4
4a. Length extended usually 50 mm or more; color marbled, darker pigmented areas random, not forming lines or rows – Pallifera marmorea (MO)
4b. Length about 20-30 mm extended; color flesh-colored to whitish, with or without blackish spots – go to 5
5a. Body ashy blue, gray, or brownish with or without an interrupted black line down the center of the mantle; length 20-30 mm extended; defense mucus translucent amber to whitish - Pallifera dorsalis (WV)
5b. Body color varies, but blackish spots present – go to 6
6a. Length about 20 mm extended; color flesh-colored to whitish, with blackish spots; defense mucus transparent amber - Pallifera fosteri (MO WV)
6b. Length 20-30 mm extended, mantle dark grey/blue with numerous scattered small round black spots, defense mucous whiteish - Pallifera secreta (WV)
Megapallifera mutabilis (Hubricht, 1951)
Pallifera dorsalis (A. Binney, 1842)
(indicated on map by asterisks - seems to be a more northerly species)
Pallifera fosteri F. C. Baker, 1939
Pallifera hempilli (W.G. Binney, 1885)
Pallifera marmorea Pilsbry, 1948
Pallifera megaphallica Grimm, 1961
Pallifera secreta (Cockerell, 1900)
Philomycus carolinianus (Bosc, 1802)
Philomycus flexuolaris Rafinesque, 1820