Perception in New Zealand mudsnails is mainly via chemical cues. In their native range, the chemical odor of predatory fish causes the snails to hide under rocks in an attempt to evade predation. They are also able to sense light.
Perception Channels: visual ; chemical
Predation on New Zealand mudsnails in North America is unknown. They are known to survive passage through the digestive tracts of some birds and fish, including mountain whitefish and rainbow trout.
However, in their native range, the snails are consumed by several species of fish and waterfowl and are infected by as many as 14 parasitic trematodes of the genus Microphallus. Levri and Lively (1996) observed the foraging behaviors of grey ducks (Anas superciliosa), mallard ducks (Anas platyrhynchos), black swans (Cygnus atratus), Canada geese (Branta canadensis), and scaups (Aythya novaeseelandiae), and they reported that grey ducks and mallard ducks are the most likely predators of NZMS.
New Zealand mudsnails that experience predation may have spines on their shells for defense against predators and may forage less frequently in the presence of predators, especially during the morning when waterfowl predators are most active.
Known Predators:
New Zealand mudsnails are shelled organisms that are either gray in color or some shade of light to dark brown. Male and female New Zealand mudsnails are very similar in physical appearance, but females are distinguished from males by the presence of developing embryos in their reproductive systems. In the western United States, the average length of the shell of the New Zealand mudsnail is 4 to 5 mm, with a maximum length of 6 to 7 mm. In their native range, the maximum length of the shell is 12 mm. The surface of the shell is characterized by right-handed coiling of 5 to 6 whorls demarcated by sulci. The shells of some individuals have a keel in the middle of each whorl and/or spines for defense against predators. A terminal oval aperture covered by a thin operculum is also present. New Zealand mudsnails may resemble snails native to the United States, but they are distinguished by their longer, narrower shells that have a greater number of whorls.
Range length: 4 to 12 mm.
Sexual Dimorphism: sexes alike
Other Physical Features: ectothermic ; bilateral symmetry
Under laboratory conditions, marked individuals were observed to survive over one year. The lifespan of New Zealand mudsnails in natural conditions is unknown.
Range lifespan
Status: captivity: 1 (high) years.
New Zealand mudsnails prefer to live in streams and the littoral zones of lakes. They prefer shallow areas but can be found up to 60 m deep. They can be found in aquatic habitats of varying substrate types, including silt, sand, gravel, cobble, and macrophyte/vegetation. Densities are highest in macrophyte habitats and lowest in silt/sand habitats. Individuals of this species live in both eutrophic and clear waters, but they thrive in disturbed or degraded waters. New Zealand mudsnails can tolerate a wide range of temperatures, from near freezing to 34ºC. The optimal salinity of the water for the snails is near 5%, but they can tolerate brackish waters and even survive salinities as high as 30 to 35% for short periods of time. New Zealand mudsnails prefer low water velocities but can be found in high velocity areas buried in the sediment or underneath cobbles and boulders.
Range depth: 60 (high) m.
Habitat Regions: temperate ; freshwater
Aquatic Biomes: lakes and ponds; rivers and streams; brackish water
Other Habitat Features: intertidal or littoral
New Zealand mudsnails (Potamopyrgus antipodarum) are native to freshwater streams and lakes of New Zealand and small, neighboring islands. However, by several speculated means of human introduction, they have become an invasive species in Australia, Europe, and North America. Occurrences of the species in North America, most of which are in the western United States, have been carefully documented since it was first discovered in Idaho. The snails are known to be established in Oregon, California, northern Arizona, New York, and Canada, affecting major freshwater systems such as Lake Ontario, Lake Erie, and Lake Superior. They also have been recently introduced in Japan.
Biogeographic Regions: nearctic (Introduced ); palearctic (Introduced ); australian (Introduced ); oceanic islands (Native )
New Zealand mudsnails are considered scrapers/grazers. Their diet consists of diatoms, epiphytic and periphytic algae, and animal and plant detritus. Therefore, they can be considered planktivores, algivores, and detrivores.
Plant Foods: algae; phytoplankton
Other Foods: detritus
Primary Diet: herbivore (Algivore); planktivore ; detritivore
In their freshwater ecosystems, New Zealand mudsnails occupy the role of scrapers/grazers and are considered to be a link between primary producers and fish. They also play a vital role in the transmission of Microphallus to ducks by serving as intermediate hosts.
New Zealand mudsnails are known to exist in extremely high densities and may comprise more than 90% of the macroinvertebrate biomass in introduced habitats. Due to their abundance, they may out-compete native mollusks and grazers for resources such as food. The decrease in the availability of resources is a likely explanation for the decline in species diversity in the presence of NZMS, the negative correlation between the NZMS population and that of mayflies, caddisflies, stoneflies, and chironomids, and the listing of five species of mollusks as endangered species. New Zealand mudsnails may also alter nutrient (carbon and nitrogen) cycling, interrupting energy flow and potentially threatening many other members of their ecosystems.
Commensal/Parasitic Species:
Because New Zealand mudsnails thrive in disturbed and degraded waters, this species can be used as an indicator of ecosystem status.
There are no direct, adverse effects of New Zealand mudsnails on humans, but control of the species is difficult and may be expensive in regions where it is not native.
New Zealand mudsnails are ovoviviparous, meaning that the development of embryos in their eggs actually occurs within the female. After completing development, the eggs hatch within the female, and the female then gives birth to the young snails. New Zealand mudsnails have been observed to grow 0.1 mm/day at 21ºC under laboratory conditions, with growth rates depending on the size of the individual. Females reach maturity at 3 to 6 months of age.
New Zealand mudsnails are not a protected species in their native range. Outside the native range, actions are being taken against the species to limit its spread as a pest.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Several aspects of the ecology of New Zealand mudsnails have contributed to their success as an invasive species. First, their tolerance of a wide range of abiotic conditions, such as temperature and salinity, aids them in transport from their native range via the ballast water of ships. Second, their escape from natural predators and parasites and their high competitive ability at the early stages of succession contribute to their establishment in introduced habitats. Third, their high fecundity, fast reproductive rate, and active and passive means of dispersal aid in their spread. Finally, their great abundance allows them to impact the ecosystem by consuming most of the primary production, dominating nutrient cycles and secondary production and decreasing populations of other mollusks and grazers.
The potential and realized negative impacts of New Zealand mudsnails have been recognized, and measures are being taken to control their spread based on what is known about their ecology. New Zealand mudsnails experience mortality when exposed to freezing or high temperatures with low humidity. It is recommended that all equipment that could be harboring the snails be frozen for several hours or be exposed to temperatures of 29 to 30ºC and low humidity for a minimum of 24 hours or temperatures greater than 40ºC and low humidity for a minimum of two hours.
New Zealand mudsnails are dioecious. Populations in New Zealand consist of sexual males and both sexual and asexual females, whereas introduced populations are comprised entirely of asexual females.
In their native range, individuals that reproduce sexually are promiscuous. During copulation, the male is found on top of the shell of a female, and the apertures of the two snails are in contact. Females can either maintain their position and proceed with mating or move in a manner that displaces the males. The duration of copulation is typically between 20 minutes and 1.5 hours. Males do not discriminate between sexual females and asexual or parasitically-castrated females, although their genes will not be passed to the offspring of the latter two types of females.
Populations found in the United States consist of triploid females that reproduce asexually by way of parthenogenesis. This type of asexual reproduction is also observed in their native range and leads to populations of genetically identical females or clones in both their native and introduced habitats.
Mating System: polygynandrous (promiscuous)
In New Zealand, reproduction typically occurs every three months. In the western United Staes, reproduction occurs throughout the year, with seasonal peaks during the months of March and October. Females reach sexual maturity at a shell length of 3 mm and produce approximately 230 young per year. Larger females produce more offspring than smaller females, and asexual females produce double the number of female offspring produced by sexual females. This species is ovoviviparous, carrying as many as 10 to 120 eggs at a time for development and giving birth to live snails. Developing embryos are sometimes present within the reproductive system of asexual females at the time of birth.
Breeding interval: In New Zealand, every 3 months.
Breeding season: Year-round
Range number of offspring: 10 to 120.
Average number of offspring: 21.6.
Range age at sexual or reproductive maturity (female): 3 to 6 months.
Key Reproductive Features: seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); parthenogenic ; sexual ; asexual ; fertilization (Internal ); ovoviviparous
This author found no published information on parental investment by New Zealand mudsnails.
Although females retain their eggs until they hatch, it's not known whether the embryos are nourished in anyway other than via the yolk created when each egg is produced.
Parental Investment: female parental care ; pre-fertilization (Provisioning); pre-hatching/birth (Protecting: Female)
The New Zealand mud snail (Potamopyrgus antipodarum) is a species of very small freshwater snail with a gill and an operculum. This aquatic gastropod mollusk is in the family Tateidae.
It is native to New Zealand, where it is found throughout the country,[3] but it has been introduced to many other countries, where it is often considered an invasive species because populations of the snail can reach very high densities.
The shell of Potamopyrgus antipodarum is elongated and has dextral coiling, with 7 to 8 whorls. Between whorls are deep grooves. Shell colors vary from gray and dark brown to light brown. The average height of the shell is approximately 5 mm ( 1 5 {displaystyle {egin{matrix}{frac {1}{5}}end{matrix}}} 
This species was originally described as Amnicola antipodarum in 1843 by John Edward Gray:
Inhabits New Zealand, in fresh water. Shell ovate, acute, subperforated (generally covered with a black earthy coat); whorls rather rounded, mouth ovate, axis 3 lines; operculum horny and subspiral: variety, spire rather longer, whorls more rounded. This species is like Paludina nigra of Quoy and Gaimard, but the operculum is more spiral. Quoy described the operculum as concentric, but figured it subspiral. Paludina ventricosa of Quoy is evidently a Nematura.[2]
This species was originally endemic to New Zealand where it lives in freshwater streams and lakes in New Zealand and adjacent small islands.[8]
It has now spread widely and has become naturalised, and an invasive species in many areas including: Europe (since 1859 in England), Australia, Tasmania, Asia (Japan,[9] in Garmat Ali River in Iraq since 2008[10]), and North America (USA and Canada: Thunder Bay in Ontario since 2001, Washington State since 2002,[11] British Columbia since July 2007[9]), most likely due to inadvertent human intervention.
Since being found in Ireland as early as 1837, Potamopyrgus antipodarum has now spread to nearly the whole of Europe. It is considered as about the 42nd worst alien species in Europe and the second worst alien gastropod in Europe.[12]
It does not occur in Iceland, Albania, Bulgaria or the former Yugoslavia.[13]
Countries where it is found include:
First detected in the United States in Idaho's Snake River in 1987, the mudsnail has since spread to the Madison River, Firehole River, and other watercourses around Yellowstone National Park; samples have been discovered throughout the western United States.[6] Although the exact means of transmission is unknown, it is likely that it was introduced in water transferred with live game fish and has been spread by ship ballast or contaminated recreational equipment such as wading gear.[20]
The New Zealand mudsnail has no natural predators or parasites in the United States, and consequently has become an invasive species. Densities have reached greater than 300,000 individuals per m² in the Madison River. It can reach concentrations greater than 500,000 per m², endangering the food chain by outcompeting native snails and water insects for food, leading to sharp declines in native populations.[21] Fish populations then suffer because the native snails and insects are their main food source.
Mudsnails are impressively resilient. A snail can live for 24 hours without water. They can however survive for up to 50 days on a damp surface,[22] giving them ample time to be transferred from one body of water to another on fishing gear. The snails may even survive passing through the digestive systems of fish and birds.[23]
Mudsnails have now spread from Idaho to most western states of the U.S., including Wyoming, California, Nevada, Oregon, Montana, and Colorado. Environmental officials for these states have attempted to slow the spread of the snail by advising the public to keep an eye out for the snails, and bleach or heat any gear which may contain mudsnails. Rivers have also been temporarily closed to fishing to avoid anglers spreading the snails.[24][25]
The snails grow to a smaller size in the U.S. than in their native habitat, reaching 6 mm (¼ in) at most in parts of Idaho, but can be much smaller making them easy to overlook when cleaning fishing gear.
Clonal species like the New Zealand mudsnail can often develop clonal lines with quite diverse appearances, called morphs. Until 2005, all the snails found in the western states of the U.S. were believed to be from a single line. However a second morph has been identified in Idaho's Snake River. It grows to a similar size but has a distinctive appearance. (It has been nicknamed the salt-and-pepper mudsnail due to the final whorl being lighter than the rest of the shell.) This morph has apparently been present in the area for several years before being identified correctly as a distinct morph of Potamopyrgus antipodarum. It dominates the typical morph where they overlap, and has a much higher prevalence of males.[26]
In 1991, the New Zealand mudsnail was discovered in Lake Ontario,[27] and has now been found in four of the five Great Lakes. In 2005 and 2006, it was found to be widespread in Lake Erie.[28] By 2006 it had spread to Duluth-Superior Harbour and the freshwater estuary of the Saint Louis River.[29] It was found to be inhabiting Lake Michigan, after scientists took water samples in early summer of 2008.[30] The snails in the Great Lakes represent a different line from those found in western states, and were probably introduced indirectly through Europe.[26]
In 2002, the New Zealand mudsnail was discovered in the Columbia River Estuary. In 2009, the species was discovered in Capitol Lake in Olympia, Washington. The lake has been closed to all public use, including boating and other recreation, since 2009.[31] A heavy cold snap in 2013, combined with a drawdown in water level in preparation, was roughly estimated to have killed 40–60% of the mudsnail population.[32][33] Other known locations include the Long Beach peninsula, Kelsey Creek (King County), Thornton Creek (King County), and Lake Washington.
In 2010, the Los Angeles Times reported that the New Zealand mudsnail had infested watersheds in the Santa Monica Mountains, posing serious threats to native species and complicating efforts to improve stream-water quality for the endangered Southern California Distinct Population Segment of steelhead.[34] According to the article, the snails have expanded "from the first confirmed sample in Medea Creek in Agoura Hills to nearly 30 other stream sites in four years." Researchers at the Santa Monica Bay Restoration Commission believe that the snails' expansion may have been expedited after the mollusks traveled from stream to stream on the gear of contractors and volunteers.[35]
As of 21 September 2010 In Colorado, Boulder Creek and Dry Creek have infestations of New Zealand mudsnails. The snails have been present in Boulder Creek since 2004 and were discovered in Dry Creek in September 2010. Access to both creeks has been closed to help avoid spread of the snails. In the summer of 2015 an industrial-scale wetland rehabilitation project was undertaken in northeast Boulder to rid the area of a mud snail infestation.
The snail tolerates siltation, thrives in disturbed watersheds, and benefits from high nutrient flows allowing for filamentous green algae growth. It occurs amongst macrophytes and prefers littoral zones in lakes or slow streams with silt and organic matter substrates, but tolerates high flow environments where it can burrow into the sediment.[4][6][36][37][38][39][40][41][42][43][44]
In the Great Lakes, the snail reaches densities as high as 5,600 per m² and is found at depths of 4–45 m on a silt and sand substrate.[4][5][6]
This species is euryhaline, establishing populations in fresh and brackish water. The optimal salinity is probably near or below 5 ppt, but Potamopyrgus antipodarum is capable of feeding, growing, and reproducing at salinities of 0–15 ppt and can tolerate 30–35 ppt for short periods of time.[4][6][45][46][47][48]
It tolerates temperatures of 0–34 °C.[4][6][49]
Potamopyrgus antipodarum is a nocturnal grazer-scraper, feeding on plant and animal detritus, epiphytic and periphytic algae, sediments and diatoms.[4][6][50][51][52][53]
Potamopyrgus antipodarum is ovoviviparous and parthenogenic. This means that they can reproduce asexually; females "are born with developing embryos in their reproductive system." Native populations in New Zealand consist of diploid sexual and triploid parthenogenically cloned females, as well as sexually functional males (less than 5% of the total population). All introduced populations in North America are clonal, consisting of genetically identical females.[6]
As the snails can reproduce both sexually and asexually, the snail has been used as a model organism for studying the costs and benefits of sexual reproduction. Asexual reproduction allows all members of a population to produce offspring and avoids the costs involved in finding mates. However, asexual offspring are clonal, so lack variation. This makes them susceptible to parasites, as the entire clonal population has the same resistance mechanisms. Once a strain of parasite has overcome these mechanisms, it is able to infect any member of the population. Sexual reproduction mixes up resistance genes through crossing over and the random assortment of gametes in meiosis, meaning the members of a sexual population will all have subtly different combinations of resistance genes. This variation in resistance genes means no one parasite strain is able to sweep through the whole population. New Zealand mudsnails are commonly infected with trematode parasites, which are particularly abundant in shallow water, but scarce in deeper water. As predicted, sexual reproduction dominates in shallow water, due to its advantages in parasite resistance. Asexual reproduction is dominant in the deeper water of lakes, as the scarcity of parasites means that the advantages of resistance are outweighed by the costs of sexual reproduction.[54]
Each female can produce between 20 and 120 embryos.[20] The snail produces approximately 230 young per year. Reproduction occurs in spring and summer, and the life cycle is annual.[4][6][8][48][55][56] The rapid reproduction rate of the snail has caused the numbers of individuals to increase rapidly in new environments. The highest concentration of New Zealand mudsnails ever reported was in Lake Zurich, Switzerland, where the species colonized the entire lake within seven years to a density of 800,000 per m².[6][57]
The parasites of this species include at least 11 species of Trematoda.[6][58] Common parasites of this snail include trematodes of the genus Microphallus.[6][59][60]
In their native habitat, these parasites sterilize many snails, keeping the populations to a manageable size. However, elsewhere in the world in the absence of these parasites, they have become an invasive pest species.[6]
Potamopyrgus antipodarum can survive passage through the guts of fish and birds and may be transported by these animals.[23]
It can also float by itself or on mats of Cladophora spp., and move 60 m upstream in 3 months through positive rheotactic behavior.[4] It can respond to chemical stimuli in the water, including the odor of predatory fish, which causes it to migrate to the undersides of rocks to avoid predation.[6][61]
The New Zealand mud snail (Potamopyrgus antipodarum) is a species of very small freshwater snail with a gill and an operculum. This aquatic gastropod mollusk is in the family Tateidae.
It is native to New Zealand, where it is found throughout the country, but it has been introduced to many other countries, where it is often considered an invasive species because populations of the snail can reach very high densities.
