( Pomacea canaliculata, Pomacea insularum )
DESCRIPTION: The shell of the channeled applesnail (Pomacea canaliculata) varies from 1.5 - 2.3 inches wide and 1.75 - 3 inches high. The shell has 5 to 6 whorls which are separated by a deep, indented suture, hence the species name 'canaliculata' or 'channeled'. The island applesnail, Pomacea insularum, appears nearly identical. The shell opening, or aperture, on both species is large and oval or round. Body color of applesnails vary from yellow to brownish black, with or without dark spiral bands. Their presence is often first noted by observation of their bright pink egg masses. These egg masses are laid on solid surfaces up to about 20 inches above the water surface. An average channeled-applesnail clutch contains 200 to 600 eggs, with each egg measuring 0.9 to 1.4 mm in diameter. An average island-applesnail clutch usually contains more than 500 eggs, slightly smaller than those of its sister species. Compared to the eggs of native applesnails, those of the invasive applesnails are smaller, pinker, and more numerous. Eggs hatch in one to two weeks, releasing hundreds of juveniles into the surrounding environment.
PATHWAYS/HISTORY: The channeled applesnail is native to temperate Argentina and northwards to the Amazon basin. Through human introduction, this applesnail has rapidly spread to Indonesia, Thailand, Cambodia, Hong Kong, southern China, Japan, Philippines, and Hawaii. There are indications that they are invading Australia. In the 1980's, channeled applesnails were introduced in Taiwan to start an escargot industry. This snail was originally imported under the name “golden snail” or “golden applesnail” for human consumption. However, the Asian escargot market never materialized and applesnails, that escaped or were released, ultimately came to cause extensive damage to rice fields. In the United States the applesnail has been introduced for use in the aquarium trade, as a food source, and for the biological control of weeds. Specimens have been collected in Alabama, Arizona, and North Carolina. Established populations exist in Florida, California, and Hawaii.
The island applesnail, P. insularum, which is native to South America, has historically been confused with the channeled applesnail, P. canaliculata, in the United States. The two species are nearly identical in appearance. However, DNA testing can confirm species identification. Invasive island applesnails have been documented in Florida, Georgia, Alabama, Texas, and Louisiana.
RISKS/IMPACTS: Invasive applesnails can spread rapidly from agricultural areas into wetlands and other natural freshwater systems where it may have a serious impact. Like all invasive species, applesnails have the potential to compete with native species for limited resources. These two snail species feed on all types of aquatic plants. Such an intense consumption of plants could alter the natural balance of a water system. Additionally, their rapid and profuse reproduction coupled with their lack of predators in the United States could make their population explode causing further problems. The channeled applesnail is a serious pest of rice throughout many countries of Southeast Asia. In the Philippines and China, it is considered the number one rice pest and has caused huge economic losses. It was introduced to Hawaii in 1989, probably from the Philippines, and for the same reasons as for its initial introduction to Southeast Asia. Again, the snails rapidly escaped or were released and quickly became major pests. Climatic modeling has shown that it has the potential to spread into uninfested parts of the world, for instance the huge rice-growing areas of India. It has already been introduced to the U.S. and threatens the major rice-crops of Texas and California.
MANAGEMENT: Once established, there is no way to eradicate all invasive applesnails. Thus, the primary management approach must be prevention. Strict quarantine must be enforced to prevent introduction and spread. In rice and taro fields, plants should be used from areas known to be snail-free. The use of a screen on water inlets may also aid in slowing the spread. A barrier of copper could be used prevent invasion. This metal is toxic to snails and they will not cross this material. Reported invasions must be eradicated rapidly while it is still possible. Once established, eradication is probably not possible. Numerous measures have been tried in attempts to control applesnails in agricultural settings. These include: widespread use of pesticides, with serious environmental and human health consequences; biological control, notably the use of fish and ducks; as well as a range of cultural and mechanical control measures. None has proven entirely effective, safe, or economically viable. In areas where the snail is damaging agricultural crops, aggressively hand picking the snails and the use of domestic carnivorous ducks has reduced the snail population by 95%. All vegetation and obstacles around fields should be removed as much as possible since the snails need this to deposit their eggs. When there are no suitable eggs-laying sites available, the snails are forced to deposit the eggs on the bare ground where they are vulnerable and easily fall into the water, which drowns the eggs.
WHAT YOU CAN DO: A similar species, Pomacea bridgesii, is a popular aquarium species that is not known to be invasive. However, this species, also non-native, is difficult to distinguish from the invasive applesnails. If you insist on keeping non-native snails, do so in an aquarium and not in outdoor ornamental ponds. Do not release any aquaria species in the natural environment. If you no longer want your pet, return it to a local pet shop for resale or trade, give it to another hobbyist, or donate it to a school, nursing home, or hospital. Remove all plant fragments, rinse any mud or debris from equipment and wading gear, and drain any water from boats before leaving an access area. The transportation of plant fragments on boats, trailers, and in live wells is one of the main introduction routes of snails and other aquatic invasive species to new lakes and rivers. General aquatic nuisance species prevention: Do not release aquarium pets or live food into the environment. Never dump live fish, e.g. bait buckets, from one body of water into another body of water. Always drain water from your boat, live well, and bilge before leaving any water access.
PROFILE CREDIT: Susan Pasko, NOAA, Anne Marie Eich, and David Britton, USFWS - IMAGE CREDIT: USFWS