Mollusks of Columbia County, Oregon

Mollusks are soft-bodied invertebrates with a hard shell and a single muscular “foot”. They include slugs, snails, clams, and mussels. Columbia County is a hotspot for terrestrial gastropods due to its wet forests, but many species are in trouble due to the loss of forest diversity.

List of all mollusks recorded in Columbia County

Terrestrial Slugs

Native slugs include the Jumping Slugs that writhe their bodies to jump an inch in the air, the Taildropper Slugs that drop the end of their tail when attacked, and the Banana Slug that can reach nearly a foot in length. There are also many introduced species.

Warty Jumping Slug – Less than 1″ long, with keel on tail and no white stripe. Hump on back with mantle visible. Only found in moist coniferous forest with decomposing logs. (photo © William Leonard)
dromedary jumping slug columbia county oregon
Dromedary Jumping Slug – About 2.5″ long. Hump on back with mantle visible. A distinct “horn” near the end of the keeled tail. Found in moist older forests with downed wood. (photo © Kristiina Ovaska)
Scarletback Taildropper oregon columbia county
Scarletback Taildropper – 1-2″ long, gray on sides and reddish above with black line between. Older mixed woodland with leaf cover and rotting wood. (photo © William Leonard)
Reticulate Taildropper oregon columbia county
Reticulate Taildropper – 1.5-2.5″ long. Dark reticulate pattern on lighter background and light line on top of tail. Found in leaf litter in disturbed forest. (photo © William Leonard)
Yellow-bordered Taildropper slug oregon columbia county
Yellow-bordered Taildropper – 2.5-3.5″. Reticulate body, yellow border on mantle and light line on top of tail. Found in wet forest with dead wood. (photo © William Leonard)
Papillose Taildropper – About 1″ long. Light brown or gray with dark lines on tail. Conical papillae cover most of body. Found in older hardwood or mixed forest. (photo © William Leonard)
Blue-gray Taildropper – 1-1.5″. Blue to dark gray with visible line where tail drops. Prefers mixed coniferous forest with deep leaf litter and downed wood. (photo © Kristiina Ovaska)
pacific banana slug columbia county oregon
Pacific Banana Slug – Up to 10″ long. Variable, with pale, yellow, or brown versions with or without dark blotches. Breathing hole near rear of smooth mantle. Found in moist forest. (photo © Jon Hakim)
Chocolate Arion slug oregon columbia county
Chocolate Arion Slug – 5-7″ long, deep red to chocolate brown. Mantle grooved with large breathing hole in middle. From Europe, now found in our forests and gardens. (photo © hromada)
Dusky Arion slug oregon columbia county
Western Dusky Arion Slug – 2-3″. Orange to brown with dark stripe on side, ID by orange-yellow mucus. Forest species introduced from Europe. (photo © William Leonard)
hedgehog arion Arion intermedius oregon columbia county
Hedgehog Slug – to 0.8″ long, yellowish or whitish with faint band, looks “prickly” when contracted. Originally from Europe but now invasive species in grassy areas. (photo © petrusvd)
Giant Garden Slug leopard oregon columbia county
Giant Garden (Leopard) Slug – 4-8″. Gray to brown with black spots and streaks. Clear mucus. Mates by hanging on branch, suspended by mucus. Introduced from Europe. (photo © William Leonard)
Three-banded Garden Slug – 2-3″. Grayish-brown with multiple broken black bands. Introduced from Europe and a pest in greenhouses and gardens. (photo © James Bailey)
Yellow Cellar Slug oregon columbia county
Yellow Cellar Slug – 3-5″. Yellowish with gray mottling and blue-gray tentacles. Yellowish mucus. Introduced from Europe and mostly associated with human areas. (photo © James Bailey)
Gray Garden Slug field milky oregon columbia county
Gray Field (Milky) Slug – 1.5-2″. Gray to tan with dark mottling. Milky white mucus. Breathing hole near rear of mantle. Found in meadows and gardens. Introduced from Europe. (photo © mc_california)
Meadow Slug Deroceras laeve oregon columbia county
Meadow (Marsh) Slug – Around 1″. Brown with smoky dark tentacles. Tail is heavily furrowed. Found in wetlands and greenhouses, originally from Palaearctic/Nearctic but now worldwide. (photo © Laura)

Terrestrial Snails

Oregon Forest Snail forestsnail columbia county oregon
Oregon Forestsnail – 1-1.5″ shell often appears weathered. Thick flared rim of the shell opening is cream. Limited to stinging nettle patches in dense broadleaf woodland. (photo © Matt D’Agrosa)
Pacific Sideband – Over 1.5″. Black band along the side of each curve. Rim of the opening is thin and non-flared. Body reddish-brown. Found in moist mixed forest. (photo © Matt D’Agrosa)
Puget Oregonian – 0.7-1″. ID by “tooth” that projects from the inner lip of shell. Found where Bigleaf Maple grow within old growth forest. Endangered Species candidate. (photo © Kristiina Ovaska)
Pygmy Oregonian snail oregon columbia county
Pygmy Oregonian – Tiny, just 0.3″ shell. Shell is covered in bristles. Has very broad tooth in inner lip of shell. Found in the debris of moist coniferous forest. (photo © William Leonard)
Northwest Hesperian – 0.4-0.7″ shell with thin, light-colored upturned lip. Shell is covered by tiny hairs that drop as it ages. Tan body. Found in moist forest. (photo © kg-)
Oregon Megomphix – 0.4-0.8″. White body and smooth, partly translucent shell. Found in low-elevation coniferous forest with Bigleaf Maple. (photo © William Leonard)
Beaded Lancetooth – 0.4-0.9″ shell. Shell opening arches down at corner. Striae cut across growth rings to give “beaded” feel. Found in variety of mixed forest. (photo © William Leonard)
Robust Lancetooth – 0.9-1.2″. Shell opening straight. Lacks “beaded” texture. Found in coniferous forest. Lancetooths feed on other snails, slugs, and worms. (photo © William Leonard)
Striated Tightcoil snail oregon columbia county
Striated Tightcoil – 0.1-0.2″ shell is slightly grooved. 6.5-7 tight coils don’t project much. Body transparent grayish. Found in moist forest. (photo © Kristiina Ovaska)

columbia vertigo oregon columbia county
Columbia Vertigo – A tiny snail less than 0.1″ high and half as wide, with 5 coils that taper on top. Found in wet forest, often climbing shrubs or small trees. (photo © William Leonard)
oblique ambershell Amber Snail oregon columbia county
Oblique Ambershell – 0.6″. Shell opening very large with 2 small coils behind main coil. Yellowish, nearly transparent shell, whitish body with black top and tentacles. (photo © Michael Skvarla)
Glossy Pillar snail oregon columbia county
Glossy Pillar – 0.2-0.3″. Long glossy shell with 5 coils ending in round tip. A worldwide species, found in gardens and other disturbed areas. (photo © Jane Trembath)
European Brown Garden Snail – 1-1.5″ shell. Black band on curves is broken and there are yellow streaks. Lacks hole in middle of whorls. Body brownish. Introduced from Europe. (photo © Joseph W Richards)
Banded Wood (Grove) Snail – 0.7-1″. Body cream to tan and lacks the hole in the middle of whorls. Usually found in urban areas. Introduced from Europe. (photo © William Leonard)
Dark-bodied Glass Snail – 0.4-0.6″. Shell opening convex. Body dark bluish above and lighter below. Feeds on young of other snails and slugs. Introduced from Europe. (photo © William Leonard)
Garlic Snail – 0.2-0.4″ Body bluish-black above. Releases garlic odor as defense. Found in very moist areas. Introduced from Europe. (photo © Alan Melville)

Freshwater Snails

Native freshwater snails prefer clean, well-oxygenated water and thus have suffered due to dams, logging, and agriculture, which cause silt to build up in streams and rivers. Most of our local species are threatened and can no longer be found in the water bodies where they once roamed. Some species that were once found in our region but are now seriously endangered include Columbia Pebblesnail, Ashy Pebblesnail, Rotund Physa, Nerite Ramshorn, and Shortface Lanx. However, the following species can still be found:

Olympia Pebblesnail oregon columbia county
Olympia Pebblesnail – 0.2-0.5″ freshwater snail found only in clean cold free-flowing streams. Heavily endangered due to dams and logging which increase the silt in its habitat. (photo © Lee Cain)
Acute Bladder Snail oregon columbia county
Acute Bladder snail – A beautiful little snail that scavenges dead plant and animal matter in almost any water body. Native to North America but now introduced worldwide. (photo © Stefan)
New Zealand Mud Snail oregon columbia county
New Zealand Mud Snail – This tiny snail (0.2″ long) from New Zealand has become a major problem, outcompeting native snails and disrupting the natural food chain. (photo © Calum McLennan)

Freshwater Mollusks

Freshwater mussels are an essential part of healthy streams, rivers, and lakes. They filter the water, helping to keep it clean, and provide food for many animals. There have been dramatic declines in freshwater mussels across the United States, likely in part due to water diversion and polluted runoff.

We have four species of native freshwater mussel in our area. It is difficult for anyone other than an expert to distinguish between the different species as each one varies in color and shape depending on the type of water it lives in as well as other factors. The following species have disappeared from many water bodies in their range and are considered to be endangered.

Western Pearlshell Oregon columbia county
Western Pearlshell – Dark on outside and beautiful purple/pink on inside. Found in cold clean forested creeks and rivers with trout or salmon populations, which their larvae hitch onto to disperse. (photo © Lee Cain)

Western Ridged Mussel Oregon columbia county
Western Ridged Mussel – A thick heavy-shelled mussel with a distinct ridge running at an angle from beak to the back. Found in sand and gravel in streams, in less rocky areas than the pearlshell. (photo © FreckLes)
Western Floater Oregon columbia county
Oregon/Western Floater – This large (5-7″) “floater” gets its name as its light shell allows it to “float” on the liquidy mud of the stagnant lakes, rivers, and sloughs where it lives. (photo © William Leonard)
California Floater Oregon columbia county
California Floater – Smaller (4-6″) and broader than the Oregon Floater. It also is found in the mud of more stagnant water bodies. Among other threats, it is eaten by invasive carp. (photo © William Leonard)
Asian Clam oregon columbia river county
Asian Clam – Small and triangular in shape, unlike native mussels. First introduced to Columbia River from Asia in the 1930s and now spread throughout the country. (photo © rojasburke)

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