New Zealand mud snail facts for kids
Quick facts for kids New Zealand mudsnail |
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| A New Zealand mudsnail seen from the right side. | |
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| Conservation status | |
Scientific classification  |
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| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| Subclass: | Caenogastropoda |
| Order: | Littorinimorpha |
| Family: | Tateidae |
| Genus: | Potamopyrgus |
| Species: |
P. antipodarum
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| Binomial name | |
| Potamopyrgus antipodarum (J. E. Gray, 1843)
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| Synonyms | |
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The New Zealand mud snail (Potamopyrgus antipodarum) is a very tiny freshwater snail. It has a special flap called an operculum that acts like a lid to seal its shell. This small aquatic creature is a type of gastropod mollusk and belongs to the Tateidae family.
This snail originally comes from New Zealand, where it lives all over the country. However, it has traveled to many other places around the world. In these new locations, it often becomes an invasive species. This means its populations can grow very large, sometimes causing problems for local plants and animals.
The New Zealand Mud Snail: A Tiny Invader
What Does the Mud Snail Look Like?
The shell of the New Zealand mud snail is long and spirals to the right. It usually has 7 to 8 whorls, which are the turns of the shell. There are deep grooves between these whorls.
The shells can be gray, dark brown, or light brown. On average, the shell is about 5 mm (about 1/5 inch) tall. The largest snails can grow to about 12 mm (about 1/2 inch). In places like the Great Lakes, they are usually 4–6 mm long.
This snail has an operculum, which is a hard "lid" that can close the shell's opening. This lid is thin and made of a horn-like material. It has a small center point from which a few spirals spread out. The opening of the shell is oval-shaped and shorter than the main spiral part of the shell.
Some mud snails have a ridge, called a keel, in the middle of each whorl. Others have special bumps or spines on their outer shell layer. These spines help protect them from predators.
Where Did the Mud Snail Come From?
This snail originally lived only in New Zealand. It was found in freshwater streams and lakes there, as well as on nearby small islands.
However, the New Zealand mud snail has now spread widely across the world. It has become a naturalized and invasive species in many areas. This spread likely happened because of accidental human activities.
Spreading Across Europe
The New Zealand mud snail was first found in London in 1859. Since then, it has spread to almost all of Europe. Experts consider it one of the worst non-native species in Europe. It is also the second worst non-native snail in Europe.
It has been found in many European countries, including:
- Great Britain (since 1859)
- Ireland
- Germany
- Poland
- The Western Baltic Sea (since 1887)
- Russia
- The Azov Black Sea region (since 1951)
- Ukraine (since 1951 in salty waters, and since 2005 in freshwaters)
- Catalonia in Spain (since 1952)
- The Mediterranean region of France (since the late 1950s)
- Italy (since 1961)
- Turkey
- The Czech Republic (since 1981)
- Slovakia (since 1986)
- Greece (since 2007)
Invading the United States
The mud snail was first found in the United States in Idaho's Snake River in 1987. Since then, it has spread to many other rivers and lakes. These include the Madison River and Firehole River near Yellowstone National Park. Samples have been found across the western United States.
Scientists believe the snails were likely brought in with water used to transport live game fish. They may also have spread through ship ballast water or on dirty fishing gear.
In the United States, the New Zealand mud snail has no natural enemies or diseases that keep its numbers in check. Because of this, it has become an invasive species. In some rivers, like the Madison River, there can be more than 300,000 snails in just one square meter. They can reach even higher numbers, over 500,000 per square meter.
These huge numbers are dangerous for the food chain. The mud snails eat the same food as native snails and water insects. This means there isn't enough food for the native species, causing their populations to drop sharply. Fish then suffer because these native snails and insects are their main food source.
Mud snails are very tough. They can live for 24 hours without water. They can even survive for up to 50 days on a damp surface. This gives them plenty of time to be carried from one body of water to another on fishing equipment. The snails can even survive passing through the digestive systems of fish and birds.
The snails have spread from Idaho to most western U.S. states. These include Wyoming, California, Nevada, Oregon, Montana, and Colorado. Environmental officials in these states are trying to slow the spread. They advise people to check their gear for snails and to freeze or heat any equipment that might have them. Some rivers have even been temporarily closed to fishing to prevent anglers from spreading the snails.
In the U.S., the snails are smaller than in their home country. They reach about 6 mm (1/4 inch) in parts of Idaho. Their small size makes them easy to miss when cleaning fishing gear.
New Zealand mud snails can have different appearances, even if they are clones. Until 2005, scientists thought all snails in the western U.S. were from one group. However, a second type, or morph, was found in Idaho's Snake River. It is similar in size but looks different. People nicknamed it the "salt-and-pepper mudsnail" because its last whorl is lighter than the rest of the shell. This new morph has been in the area for several years. It tends to be more common than the typical morph where they live together.
In 1991, the New Zealand mud snail was found in Lake Ontario. It has now been found in four of the five Great Lakes. By 2005 and 2006, it was widespread in Lake Erie. By 2006, it had reached the Duluth-Superior Harbour and the Saint Louis River estuary. In 2008, scientists found it in Lake Michigan. The snails in the Great Lakes are from a different group than those in the western states. They likely arrived indirectly through Europe.
In 2002, the mud snail was found in the Columbia River Estuary. In 2009, it was discovered in Capitol Lake in Olympia, Washington. The lake has been closed to all public use since 2009. In 2013, a severe cold snap and lower water levels were estimated to have killed 40–60% of the mud snail population there. Other places where they are found include the Long Beach peninsula, Kelsey Creek, Thornton Creek (both in King County), and Lake Washington.
By 2010, the Los Angeles Times reported that the New Zealand mud snail had infested rivers in the Santa Monica Mountains. This posed serious threats to native species. It also made it harder to improve water quality for the endangered steelhead fish. The snails spread from Medea Creek in Agoura Hills to almost 30 other streams in just four years. Researchers believe the snails spread quickly on the gear of workers and volunteers.
In Colorado, Boulder Creek and Dry Creek have had mud snail infestations since 2004 and 2010, respectively. Access to both creeks has been closed to help stop the snails from spreading. In the summer of 2015, a large project was started in northeast Boulder to remove a mud snail infestation from a wetland area.
How Does the Mud Snail Live?
Where Mud Snails Live
The snail can handle muddy water and thrives in areas where the environment has been disturbed. It also benefits from lots of nutrients in the water, which helps green algae grow. It lives among water plants and prefers shallow areas in lakes or slow-moving streams. These places usually have mud and decaying plant matter on the bottom. However, it can also live in fast-flowing water by burrowing into the sediment.
In the Great Lakes, these snails can reach densities of up to 5,600 per square meter. They are found at depths of 4–45 meters on muddy and sandy bottoms.
This species can live in both fresh and slightly salty water. It grows best in water with low salt levels (around 5 parts per thousand or less). However, it can eat, grow, and reproduce in salt levels up to 15 parts per thousand. It can also survive in very salty water (30–35 parts per thousand) for short times. It can live in temperatures from 0–34 °C (32–93 °F).
What Mud Snails Eat
The New Zealand mud snail is a grazer-scraper. This means it feeds on tiny bits of plants and animals that have died. It also eats algae that grow on surfaces, sediments, and tiny plant-like organisms called diatoms.
The Mud Snail Life Cycle and Reproduction
New Zealand mud snails are ovoviviparous, meaning their eggs hatch inside the mother, and she gives birth to live young. They are also parthenogenic, which means females can reproduce without a mate. They essentially create clones of themselves.
In their native New Zealand, some populations have females that reproduce sexually and others that reproduce asexually. There are also males, but they make up less than 5% of the population. However, all the mud snails found in North America are clones, meaning they are genetically identical females.
Because these snails can reproduce both with and without a mate, they are studied to understand the pros and cons of sexual reproduction. Asexual reproduction allows every snail to have babies and avoids the need to find a partner. But, asexual offspring are clones, so they all have the same traits. This makes them vulnerable to parasites. If a parasite can overcome one snail's defenses, it can infect the entire population.
Sexual reproduction mixes up genes, creating unique combinations of defense genes in each offspring. This variety means that no single parasite can easily wipe out the whole population. New Zealand mud snails often get infected by trematode parasites. These parasites are common in shallow water but rare in deeper water. As expected, sexual reproduction is more common in shallow water, where parasite resistance is important. Asexual reproduction is more common in deeper lake waters, where there are fewer parasites. In these areas, the benefits of sexual reproduction are outweighed by the effort it takes to find a mate.
Each female snail can produce between 20 and 120 young. A snail can produce about 230 young each year. Reproduction happens in spring and summer, and the snails usually live for about a year. Their fast reproduction rate has caused their numbers to grow quickly in new places. The highest number of New Zealand mud snails ever recorded was in Lake Zurich, Switzerland. There, the species took over the entire lake in seven years, reaching 800,000 snails per square meter.
Natural Controls and Other Relationships
The parasites of the New Zealand mud snail include at least 11 types of Trematoda. Common parasites include trematodes from the genus Microphallus.
In their native New Zealand, these parasites stop many snails from having babies. This helps keep the snail populations at a manageable size. However, in other parts of the world, without these parasites, the snails have become an invasive pest.
Potamopyrgus antipodarum can survive being eaten and passing through the digestive systems of fish and birds. This means these animals can accidentally transport the snails to new places.
The snails can also float on their own or on clumps of algae. They can move upstream about 60 meters in three months by actively swimming against the current. They can sense chemicals in the water, including the smell of fish that might eat them. When they detect predators, they move to the underside of rocks to hide.
See Also
- Invasive species of New Zealand origin
Images for kids
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right side view of Potamopyrgus antipodarum
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