Chinese Mystery Snail

The shells of Chinese mystery snails are thick and rounded and can reach lengths of 6 -7 cm. Theses shells are typically olive green in colour but can range from muted shades of greenish brown to reddish brown. Their shells have distinct sutures (lines separating whorls on the shell), with 6-7 whorls, and an oblong shaped operculum which acts like a lid, deterring predators and protecting them from harsh environmental stressors. Females of this species are typically longer lived than the males, and therefore will often grow larger (Kingsbury, S. E., McAlpine, D. F., Cheng, Y., Parker, E., & Campbell, L. M., 2021). The banded mystery snail is another invasive look-a-like species but can be differentiated by 3-4 dark brown spiral bands (Ontario Federation of Anglers and Hunters Invading Species Awareness Program, n.d).

The Chinese mystery snail will grow rapidly within the few first spans of its life, reaching sexual maturity after only 6-12 months (Kingsbury, S. E., McAlpine, D. F., Cheng, Y., Parker, E., & Campbell, L. M., 2021). These fast growth rates and robust size allows them to avoid predation once fully grown. The Chinese mystery snail is one of the biggest freshwater snails in its family, Viviparidae, and is larger than any other native freshwater gastropod in the Great Lakes. Under ideal habitat conditions, females of this species will typically live longer than males, although both sexes have been recorded to reach lengths surpassing 5cm (Kingsbury, S. E., McAlpine, D. F., Cheng, Y., Parker, E., & Campbell, L. M., 2021).

Once mature, female Chinese mystery snails deliver fully formed and shelled offspring, born with 3–5 mm shell diameters. Throughout June to late October in their non-native North American range, these mature females reproduce numerous times, with just a single female capable of producing an average of 25-35 offspring per brood, (Kingsbury, S. E., McAlpine, D. F., Cheng, Y., Parker, E., & Campbell, L. M., 2021). In addition, Chinese mystery snails demonstrate increased reproduction in warmer water temperatures (around 27°C), while snails held at cooler water temperatures (12°C or below), displayed limited or discontinued reproduction (Kingsbury, S. E., McAlpine, D. F., Cheng, Y., Parker, E., & Campbell, L. M., 2021).

Chinese mystery snails live in various freshwater aquatic ecosystems but thrive in disturbed watersheds with slow-moving currents and sandy/muddy substrate, where they can burrow themselves or hide (Edgar MR, Hanington PC, Lu R, Proctor H, Zurawell R, Kimmel N, Poesch MS, 2022). The most preferred habitat of the Chinese mystery snail includes lakes, rivers, and ponds, but sightings have also been reported in marshes, bays, ditches, and harbors. They favor habitats with water depths of 3 m or less, and dislike deeper rivers with strong currents. Chinese mystery snails also display a wide thermal tolerance and are estimated to be capable of withstanding water temperatures ranging from 0°C – 45 °C (Kingsbury, S. E., McAlpine, D. F., Cheng, Y., Parker, E., & Campbell, L. M., 2021).

Believed to be introduced into North America during the late 1800s as an addition to the Asian food market, and the aquarium trade, the first Canadian Chinese mystery snail wild sighting took place in 1905 at St. John’s, Newfoundland (Kingsbury, S. E., McAlpine, D. F., Cheng, Y., Parker, E., & Campbell, L. M., 2021). Today, Chinese mystery snails have invaded numerous provinces throughout Canada with the current exception of Manitoba, Labrador, Yukon, Nunavut, and Northwest Territories. Among documented invasions of Chinese mystery snails in Canada, the province of Ontario holds the highest reported number of sightings, putting the health of its aquatic ecosystems at high risk.

Ecological Impacts

The large relative size, multiple feeding mechanisms (consuming algae & filter feeding for plankton), resistance to predation, and ability to withstand environmental stressors, such as fluctuating water temperatures and dry conditions enable the Chinese mystery snail to easily out-compete native freshwater gastropods and mollusks. In turn, this ability to out-compete native species negatively affects the biodiversity of aquatic ecosystems, and alters food webs by decreasing the population sizes of common mollusk prey species for predators such as otters, muskrats, waterfowl, fishes, etc. In addition, the Chinese mystery snail alters nutrient cycling by excreting large amounts of fecal matter, which can alter the nitrogen and phosphorous cycling within aquatic ecosystems and can cause impacts on bacterial, algal, and zooplankton communities.

Economic & Social Impacts

Like invasive zebra mussels and quagga mussels, the presence of the Chinese mystery snail in freshwater aquatic ecosystems can lead to water quality issues such as algal blooms. This effect is produced by the high filtration rate of plankton the Chinese mystery snail displays when feeding. The absence of plankton and free-floating detritus in the water produces elevated water clarity, which may seem like a positive side effect, but leads to excess sunlight penetration, generating excess photosynthesis, and ultimately results in overrun algal blooms. Chinese mystery snails also have the potential to be a vector for parasites and diseases and have been reported to clog water intake pipes. Their empty large decaying shells can also wash up on shore, discouraging recreational activities, and could create hazards if stepped on.

Molluscicides, commonly employed to manage invasive mollusk populations such as rotenone and copper sulfate, have proven to be ineffective in the control of Chinese mystery snails (Kingsbury, S. E., McAlpine, D. F., Cheng, Y., Parker, E., & Campbell, L. M., 2021). Similarly, waterbody modification such as water draining would also likely fail as a control strategy due to Chinese mystery snails’ capability to remain out of water for extended weeks at a time. This ability can also help facilitate the long-distance spread of this invader from one waterbody to another via overland transport. Therefore, physical removal and preventative actions are the most promising controls for this resilient invader.

If Chinese Mystery Snails are spotted in a waterbody outside of their native range, if possible, they should be removed and disposed of far away from that waterbody, in a suitable compost or garbage bin.  Whether alive or dead, aquatic pets should never be released into a wild environment, as they have the potential to spread diseases or become invasive and out complete native species for natural resources.

All watercraft and equipment should always be cleaned thoroughly after exiting any waterbody, and live wells and bilges drained on land. This simple practice ensures boaters are not hitching aquatic invasive species such as the Chinese mystery snail from one waterbody to another, and in turn, will help limit the spread of this destructive invader.