Faucet snail (Bithynia tentaculata)

Synonyms: Helix tentaculata, Bulimus tentaculatus, Bithynia tentaculata tentaculata

Common Names: Mud bithynia, mud snail

Description:

Faucet snail (Bithynia tentaculata) is a small freshwater snail from Europe that reached the Great Lakes in the 1870s, probably carried in the solid ballast or packing material of timber ships [1]. MISIN tracks it because it does real harm: it carries parasitic worms that have killed well over 100,000 ducks and coots in the Great Lakes and Upper Mississippi River, and it crowds out native snails and clogs water intake pipes [1]. It now lives in lakes, ponds, and rivers across the region [1].

Identification:

The faucet snail is small ? its shiny, pale brown, oval shell grows to only about half an inch (12?15 mm) and coils in five to six whorls [1]. The most useful clue is the "trapdoor" that seals the shell opening (an operculum): in the faucet snail it is white and hard, teardrop- to oval-shaped, and marked with fine concentric rings, like the rings of an onion or a tiny fingerprint [1]. The shell opening sits on the right side when you hold the shell with the tip pointing up [1]. The living snail has long, slender tentacles [1].

Because it lives underwater and is small, the faucet snail is easy to miss. It is most likely to be found on rocks, wood, plants, and mud in shallow water, on boats and gear pulled from infested waters, or when biologists sort bottom samples ? and dead waterbirds in spring or fall can be a sign that infected snails are present [1]. Positive identification of these small snails usually needs a hand lens and an expert [1].

At-a-glance cues:

1. Small, shiny, pale brown oval shell up to about half an inch (12?15 mm), with 5?6 whorls [1]
2. Hard white "trapdoor" (operculum) that is teardrop- to oval-shaped with fine concentric rings [1]
3. Shell opening on the right side when the tip points up [1]
4. Found in shallow fresh water on rocks, wood, plants, and mud [1]

Habitat:

The faucet snail lives in freshwater ponds, shallow lakes, slow rivers, and canals [1]. It crawls over firm surfaces and aquatic plants and is usually found in shallow water down to about 16 feet (5 m) deep [1]. It feeds in two ways ? scraping algae off surfaces and filtering tiny food particles from the water ? which helps it do well in a range of conditions [1].

The snail is native to Europe, from Scandinavia south to Greece [1]. In North America it has spread across the Great Lakes region and the Northeast since the 1870s, and it is now established in lakes and rivers from Quebec and Wisconsin to Pennsylvania and New York, as well as the Upper Mississippi River [1]. It tolerates a fairly wide range of water hardness and acidity, which has helped it colonize many water bodies [1].

Reproduction:

The faucet snail spreads from water to water mostly by hitching a ride with people. The snails and their eggs can cling to boats, trailers, motors, anchors, fishing gear, waders, and aquatic plants, and to bait buckets and other containers of lake water [1]. The faucet snail is especially good at surviving the trip because it can pull in and seal its shell with its trapdoor, letting it stay alive out of water for days [1].

Unlike many snails, the faucet snail has separate males and females [1]. Females glue their eggs in neat double rows onto rocks, wood, plants, and even other snails' shells, mainly in late spring and early summer and again in fall, in batches of up to several dozen, and a single female can lay up to about 350 eggs in her life [1]. Eggs hatch in roughly three weeks to three months depending on water temperature, and the snails live about one and a half to three years [1]. This steady output lets a few snails build into a dense population quickly, so stopping their spread between waters is the most important step (see Management) [1].

Impact and Damage:

The faucet snail is not dangerous to handle, but it is one of the more harmful aquatic snails because of the parasites it carries. It is the intermediate host for three kinds of parasitic flatworms (trematodes) ? and when ducks, coots, and other waterbirds eat infected snails, the parasites cause fatal internal bleeding [1]. These die-offs are large and recurring: faucet snail parasites have been linked to well over 100,000 waterbird deaths across the Great Lakes and Upper Mississippi River, with thousands of birds dying in single events during spring and fall migration [1].

The snail also harms native wildlife and infrastructure. It out-competes native snails for food and space ? at Oneida Lake in New York its arrival was tied to about a 15% drop in the variety of native mollusks ? and dense populations can foul and clog municipal water intake pipes [1]. For a homeowner on a lake, that means a snail that can foul gear and water systems; for natural area stewards, it means a driver of waterbird mortality and native-snail decline that is very hard to remove once established [1].

Similar species:

Several small freshwater snails can be mistaken for the faucet snail, and the shape of the "trapdoor" (operculum) is the best way to tell them apart ? telling these snails apart usually takes a hand lens and an expert.

European valve snail (Valvata piscinalis) is a similar small introduced snail, but its shell is a lower, rounder beehive shape and its trapdoor is marked with a tight spiral of about ten turns rather than the faucet snail's concentric onion-like rings.

Mud and spire snails (family Hydrobiidae) are native operculate snails of similar size, but most have taller, narrower, cone-shaped shells and are far smaller and plainer than the faucet snail's stout oval shell.

Mystery snails (Cipangopaludina spp.) also have a trapdoor with concentric rings, but they are much larger ? often 1.5 to 2.5 inches tall ? so size alone separates them from the half-inch faucet snail.

Monitoring and rapid response:

Signs to watch for:

1. Small, shiny, pale brown oval snails (about half an inch) with a hard white "trapdoor" on rocks, wood, plants, and mud in shallow fresh water [1]
2. Snails or eggs in neat double rows on gear, boats, anchors, or plants pulled from a lake or river [1]
3. Die-offs of ducks and coots during spring or fall migration, which can signal infected snails nearby [1]

What you can do:

1. Clean, Drain, and Dry ? before leaving a launch, remove all plants, mud, and animals from your boat, trailer, motor, anchor, and gear; drain every bit of water from the bilge, live wells, and bait buckets; and dry everything thoroughly, since this snail can survive out of water by sealing its shell [1].
2. Never move water, plants, bait, or aquarium contents from one water body to another, because the snails and their eggs travel in all of these [1].
3. If gear can't be fully dried between trips, rinse it well away from any water body; freezing equipment solid also kills the snails [1].
4. Natural area crews and lake associations can survey new and connected waters, focus on early detection at boat launches, and decontaminate boats, waders, and sampling gear between sites to avoid carrying the snail and its parasites [1].
5. Report sightings (below) ? because the faucet snail looks like several harmless native snails, photos and a sample for an expert are especially helpful [1].

When to call a professional:

1. A suspected new population ? especially in a water body not known to have it, or a local waterbird die-off ? contact your state aquatic invasive species program or a regional Sea Grant office for confirmation and guidance [1].
2. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Bithynia tentaculata (Linnaeus, 1758) ? Faucet Snail / Mud Bithynia (Species Profile). nas.er.usgs.gov

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