Chinese mystery snail (Cipangopaludina chinensis)

Common Names: Oriental mystery snail, trapdoor snail, Asian apple snail, Chinese vivipara

Description:

Chinese mystery snail (Cipangopaludina chinensis) is a large freshwater snail native to eastern Asia that was brought to North America through the food and aquarium trades starting in the late 1800s [1]. It now lives in lakes, ponds, and slow rivers across much of the United States [1]. MISIN tracks it because it hitchhikes between waters on boats and gear, builds up to high numbers, crowds out native snails, and can carry parasites [2][4].

Identification:

The Chinese mystery snail is a big, rounded freshwater snail. Its coiled shell grows up to about 2 to 3 inches tall ? larger than most native pond snails ? with 6 to 7 smooth, tightly wound turns and no stripes or bands [1][3]. The shell is olive-green to brownish and is often coated with a layer of algae or muck that makes it look mossy [1]. Its most telling feature is a hard "trapdoor" (a plate called an operculum) that seals the shell opening when the snail pulls inside; you will see this door on a live snail, but it is missing from an empty shell [2].

Look for these snails from spring through fall in shallow, calm water, where they graze on the bottom, on plants, and on docks and rocks [1]. Late summer is often when people first notice them: large numbers can die off at once, washing piles of empty shells onto beaches and shorelines [2].

At-a-glance cues:

1. Large rounded shell, about 2 to 3 inches tall, with 6 to 7 smooth whorls and no bands [1][3]
2. Olive-green to brown color, often coated with algae or muck so it looks mossy [1]
3. A hard "trapdoor" (operculum) seals the opening on live snails; absent from empty shells [2]
4. Piles of empty shells washed up on a beach after a summer die-off [2]

Habitat:

Chinese mystery snails are native to eastern Asia, from Southeast Asia north to Japan and eastern Russia [1]. In North America they were first recorded in the early 1900s and have since spread to lakes and rivers in more than 40 states, including the Great Lakes region [1].

They prefer shallow, quiet fresh water ? ponds, lakes, marshes, ditches, canals, and slow-moving rivers ? with soft, muddy or silty bottoms where they can graze [1]. They tolerate a wide range of conditions, which helps them settle into many kinds of water bodies once they arrive [4].

Reproduction:

This snail most often reaches a new lake or pond by hitching a ride. People spread it by releasing unwanted aquarium or water-garden snails into the wild, and by moving boats, trailers, anchors, ropes, and fishing gear from one water body to another without cleaning them [2][3]. Newly born snails can be as small as a grain of rice, so they are easy to move without noticing [3]. The snail is also remarkably tough out of water ? it can survive for weeks by sealing itself behind its trapdoor, which lets it ride along on dry equipment between trips [4].

Chinese mystery snails have separate males and females, and females give birth to live, fully formed young rather than laying eggs [1]. A single female can carry well over 100 developing young at once and keeps producing them through the warm months, so a few snails can grow into a dense population within a few years [1]. Females can live up to about five years [1].

Impact and Damage:

For people, the main concerns are health and nuisance. Chinese mystery snails can carry parasites and other organisms that may affect people, pets, and wildlife, so they should not be eaten or handled carelessly [1][4]. They also clog the intake screens of water pipes used for irrigation and other purposes [1]. When large numbers die off at once ? often in late summer ? the rotting snails and piles of empty shells foul beaches and shorelines with odor and litter [1][2].

In natural areas, these snails reach very high densities and compete with native snails for food and space [4]. Because they are large, well armored, and hard for predators to eat, they can out-compete and displace native snails, reducing their numbers over time [4]. By grazing heavily on the bottom, dense populations can also shift the balance of the aquatic food web [1]. In some settings the snails take up heavy metals and other pollutants, which can move into animals that eat them [1].

Similar species:

Several other trapdoor snails can be mistaken for the Chinese mystery snail.

Japanese mystery snail (Cipangopaludina japonica) is the closest match ? also large, non-native, and trapdoor-sealed, and the two often live in the same waters. Its shell is taller and more sharply pointed with more shouldered whorls, while the Chinese mystery snail is rounder and more globe-shaped [1].

Banded mystery snail (Callinina georgiana) is another trapdoor look-alike, but it is usually smaller and shows reddish-brown bands spiraling across the shell, which the Chinese mystery snail never has [1].

Trapdoor snails in the genus Campeloma are native snails that also seal their opening with a door, but they are smaller and more slender and lack the mossy, algae-coated look of a mystery snail [1].

Apple snails (Pomacea species) share the trapdoor and big size, but their shells are rounder and more ball-shaped and they are mainly a concern in warmer southern waters [1].

Monitoring and rapid response:

Signs to watch for:

1. Large olive-green to brown snails, up to 2 to 3 inches tall, grazing in shallow water, on plants, or on docks from spring through fall [1]
2. A hard trapdoor sealing the shell opening on live snails [2]
3. Piles of empty shells washed onto a beach or shoreline, often after a late-summer die-off [2]

What you can do:

1. Never release aquarium or water-garden snails into ponds, lakes, streams, or storm drains; this is the most common way they spread [2][3]
2. Hand-pick snails and empty shells from your shoreline, dock, and gear, then bag them and put them in the trash ? do not toss them back in the water [3]
3. Clean, Drain, Dry: before moving a boat, trailer, dock, lift, or any gear to another water body, remove all plants, mud, and animals, drain all water, and let everything dry for several weeks, since these snails survive a long time out of water [2][4]
4. For lake associations and natural area crews: survey shorelines, focus first on small or newly found infestations and isolated ponds where removal is still realistic, organize hand-removal events, and post Clean-Drain-Dry signs at boat launches [4]

When to call a professional:

1. Large, established populations across a whole lake or pond ? there is no proven way to control this snail once it is widespread, so work with your lake association or aquatic invasive species program [4]
2. Snails clogging water-intake pipes, irrigation lines, or other equipment [1]
3. Any whole-waterbody treatment ? partner with a land manager or state aquatic invasive species program before acting
4. 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. Cipangopaludina chinensis (Gray, 1834) ? Species Profile. nas.er.usgs.gov
2. Minnesota Department of Natural Resources. Chinese Mystery Snail (Cipangopaludina chinensis). dnr.state.mn.us
3. University of Illinois Extension. Chinese Mystery Snail, Invasive Species. extension.illinois.edu
4. Kingsbury SE, McAlpine DF, Cheng Y, Parker E, Campbell LM (2020). "A review of the non-indigenous Chinese mystery snail, Cipangopaludina chinensis (Viviparidae), in North America, with emphasis on occurrence in Canada and the potential impact on indigenous aquatic species." Environmental Reviews 29(2):182?200. semanticscholar.org

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