European valve snail (Valvata piscinalis)

Synonyms: Nerita piscinalis, Valvata piscinalis antiqua, Cyclostoma obtusum

Common Names: European stream valvata, European stream valve snail, valve snail

Description:

European valve snail (Valvata piscinalis) is a tiny freshwater snail from Europe and western Asia that reached the Great Lakes more than a century ago [1]. It was first found in Lake Ontario in the 1890s, likely arriving in packing material made of straw and marsh grasses, and has since spread through several lakes and rivers in the Northeast [1]. MISIN tracks it as a non-native snail that could compete with native snails, though its effects in North America are still poorly understood [1][2].

Identification:

The European valve snail is very small ? its rounded, beehive-shaped shell reaches only about 5 mm tall in the Great Lakes (up to 7 mm in Europe), roughly the size of a peppercorn [1]. The shell coils in four to five whorls and is white to beige, often with an orange-to-reddish tint at the tip [1]. The opening can be sealed by a small round "trapdoor" (an operculum) marked with about ten tight spiral turns ? a useful clue under a hand lens [1]. The living snail is yellowish with gray-and-white speckles, blue eyes, and a darker snout, and when active it shows a feathery external gill and a slender thread-like tentacle [1].

Because it is so small and lives underwater, this snail is rarely noticed by casual observers. It is most likely to turn up when biologists sort through bottom samples, or when it shows up on aquatic plants, mud, and sand in lakes, streams, and rivers ? it lives from the shallows down to about 75 feet (23 m) deep [1]. Positive identification usually needs a microscope and an expert [1].

At-a-glance cues:

1. Tiny rounded, beehive-shaped shell only about 5 mm tall (peppercorn-sized), with 4?5 whorls [1]
2. White-to-beige shell, often with an orange-red tint at the tip [1]
3. Round "trapdoor" (operculum) marked with roughly 10 tight spiral turns [1]
4. Living snail is yellowish with gray-white speckles and blue eyes, with a feathery gill when active [1]

Habitat:

The European valve snail lives in lakes, streams, and rivers, where it crawls over mud, silt, sand, and aquatic plants [1]. It does best in cool, clear, nearshore waters that are not heavily enriched with nutrients, and it uses underwater plants as places to lay its eggs [1]. It can handle a range of calcium levels and survives winter buried in mud, and in the Great Lakes it has been found from the shallows down to about 75 feet (23 m) deep [1].

The snail is native to Europe, the Caucasus, western Siberia, and central Asia [1]. In North America it has established across the Great Lakes region and parts of the Northeast ? including Lake Ontario, Lake Erie, the St. Lawrence and Hudson Rivers, Lake Champlain, and Cayuga Lake ? and it now occurs across the Great Lakes states and provinces [1]. It grazes on tiny plant and animal matter and, unlike most native snails, can also filter food particles from the water [1][2].

Reproduction:

The European valve snail spreads from water body to water body mostly with human help. Early on it likely arrived in shipping materials, and its later spread has been aided by canals and by ships moving between lakes [1]. On a smaller scale, the snails and their eggs can hitch a ride on boats, trailers, fishing gear, bait buckets, and aquatic plants carried from one lake to another [1]. There is no floating larval stage, so it cannot drift far on its own ? moving water, boats, and gear do the work [1].

This snail is a hermaphrodite ? each individual has both male and female parts [1]. It grows fast and breeds heavily, spawning two to three times a year and laying up to about 150 eggs at a time in jelly-like clutches stuck to underwater plants [1]. Eggs hatch in roughly 15 to 30 days, the snails breed at about one year old, and most live only about 13 to 21 months [1]. This quick turnover lets populations build rapidly once the snail reaches suitable water, which is why preventing its spread between lakes is the main line of defense (see Management) [1].

Impact and Damage:

The European valve snail is not known to harm people, pets, or property ? it is a tiny underwater grazer with no reported health or economic effects in North America [1]. Honest assessment is limited, though: scientists say the research needed to judge its impact in the Great Lakes is still inadequate [1].

The main ecological concern is competition with native snails. The European valve snail can be an early colonizer of disturbed waters, and unlike most native snails it can filter food from the water as well as graze, which could let it become abundant where conditions favor it [1][2]. At Oneida Lake in New York, native snails in the family Hydrobiidae appeared to decline after it arrived, possibly because of competition, though this link is not firmly proven [1]. So far there is little or no documented evidence of broader harm, and the species is best treated as one to watch and to keep from spreading rather than one with proven large-scale impact [1].

Similar species:

Several tiny freshwater snails can be mistaken for the European valve snail, and telling them apart usually takes a hand lens or microscope and an expert.

Native valve snails (Valvata spp.) are close relatives in the same family and look very similar; some native species have raised ridges (keels) on the shell, and shell shape and the spiral pattern on the trapdoor are used to separate them.

Faucet snail (Bithynia tentaculata) is another small introduced freshwater snail with a trapdoor, but its shell is more pointed and cone-shaped and its trapdoor shows concentric growth rings rather than the European valve snail's tight spiral of about ten turns.

Mud and spire snails (family Hydrobiidae) are similarly tiny operculate snails, but most have taller, more slender, cone-shaped shells rather than the European valve snail's low, rounded, beehive shape.

Monitoring and rapid response:

Signs to watch for:

1. Tiny rounded, beehive-shaped snails (about 5 mm) on aquatic plants, mud, or sand, or in bottom samples from lakes, streams, and rivers [1]
2. Small snails or jelly-like egg clutches on plants, gear, or boats pulled from infested waters [1]
3. New occurrences in waters connected by canals or heavy boat traffic [1]

What you can do:

1. Clean, Drain, and Dry ? before leaving a launch, remove plants, mud, and animals from your boat, trailer, motor, and gear; drain all water from the bilge, live wells, and bait buckets; and let everything dry completely before entering another water body [1].
2. Never move water, plants, bait, or aquarium contents from one lake or stream to another, since the snails and their eggs travel in all of these [1].
3. If you keep a home aquarium or water garden, never release its plants, snails, or water into a natural water body [1].
4. Natural area crews and lake associations can survey new and connected waters, focus on early detection at boat launches, and decontaminate sampling gear, waders, and boats between sites to avoid carrying the snail and other aquatic invaders [1].
5. Report sightings (below) so new occurrences can be confirmed ? this snail is easily confused with native snails, so photos and a sample for an expert help [1].

When to call a professional:

1. A suspected new population, especially in a water body not known to have it ? 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. Valvata piscinalis (O.F. Muller, 1774) ? European Stream Valvata (Species Profile). nas.er.usgs.gov
2. Grigorovich IA, Mills EL, Richards CB, Breneman D, Ciborowski JJH (2005). "European valve snail Valvata piscinalis (Muller) in the Laurentian Great Lakes basin." Journal of Great Lakes Research 31(2):135?143. semanticscholar.org

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