Photographer:Dr. Matthew McClure Source: Matthew McClure, TISI, Lamar State College-Orange Location: Armand Bayou, Pasadena, TX
Adult Description: Pomacea maculata is a large-sized snail. The globular-shaped shells can have a wide variation of color with banded patterns of black, brown, green, or yellow. Their bodies can be 6cm wide to 8 cm tall with the shell extending up to 15cm.
Egg Description: Bright reddish-pink eggs are laid on rice plants in groupings of 200-600. The eggs are bright red due to their high levels of carotenoid components. Eggs are laid above the water level, and are easier to identify then the submerged adult snails.
The aggressive and successful invasion of the channeled apple snail in irrigated rice systems in many parts of Asia have led to significant economic damages. Direct-seeded rice suffers significantly more damage than trans-planted rice, because golden snails consume greater amounts of the younger, more succulent plants. Snail damage in uncontrolled fields can be as high as 100% for rice seedlings in the germinating stage, as opposed to 20% on average in the transplanting stage. Overall most rice varieties tend to be directly seeded as opposed to transplanted, making them more susceptible to Pomacea maculata. Farmers in the infested areas are faced with the options of paying additional costs to control the spread of snails, replanting damaged areas of paddy, or ignoring the problem all together at the risk of potentially large yield losses. Since Pomacea maculata has been documented in Texas since at least 1990 it poses a serious ecological and economical threat to the 22 counties that produce rice in Texas. Also, Pomacea maculata transmits the Rat lungworm Angiostrongylus cantonensis which can infect humans if they eat raw or undercooked Pomacea maculata. The parasite Angiostrongylus cantonensis causes eosinophilic meningitis, and while it is not completely fatal in humans, if it goes undetected it will slowly destroy or scar the human brain.
The snail, indigenous to South America, was introduced into Taiwan from Argentina for commercial production in the 1980s. From Taiwan, the snail was distributed to developing countries to help the rural poor earn additional income through backyard rearing and to supplement protein in their diets. The snail was introduced without prior studies on market demands or its impact on the ecosystem. The snail has spread from South America to Southeast Asia and reached Hawaii in the 1990s. In Hawaii, has caused significant damage to taro even destroying the crop before harvest. Mainly due to the apple snails in 2003, fields of taro for processing reached a record low of 4.8 million pounds, down 17% from the previous year. It is successfully transmitting Angiostrongylus cantonensis in Hawaii. In the early 1980s, Pomacea maculata was released in southern Florida probably by persons within the tropical pet industry. It has since spread throughout the southeastern United States. Populations of this snail have tested positive for the nematode in New Orleans, LA. Thankfully, they have remained isolated, and there have been no cases of human Angiostongylus cantonensis infections.
South America, namely Argentina
U.S. Present: AL, AZ, CA, FL, GA, HI, LA, NC, SC, TX and VA. Records of this snail are not consistent and it may be far more established within the United States.
U.S. Habitat: Naturally in slow-moving streams and ponds but has found refuge in rice paddies all over Southeast Asia. This means that lakes, slow-moving streams and rice fields are potentially threatened by this snail.
Texas: This snail species has been present in Texas for over 20 years. Populations have been found in southeastern Texas near Fort Bend, Harris and surrounding counties.
Except for genetic testing, the channeled apple snail is not able to be physically differentiated from its close relative, Pomacea canaiculata. Due to the physical confusion of the snails “in the field” the distribution of both Pomacea species may have been confused over the years.
Management of apple snails has generally achieved good results in transplanted rice fields in Japan. Snails do not feed on transplanted rice in shallow water. Keeping paddy water shallow thus helps to control snail damage and is now the most commonly used management practice. Transplanting older rice is also effective because rice gradually becomes tolerant to the snails as it grows. Using these practices, with occasional pesticide applications, snails can be reasonably well controlled in transplanted rice. However, in poorly leveled paddy fields or in regions where very young seedlings are transplanted, the apple snail still remains an important rice pest, which can be very difficult to control.
Management in the United States:
As it seems to be with most invasive species, the channeled apple snail is sold in the trade industry and despite any management the snail cannot be fully controlled until it is not allowed to be sold in the pet trade. Never release applesnails from aquaria into the wild (FFWCC 2006).
In Texas, the removal of adult applesnails from any habitat is prohibited. This is to prevent the accidental spread of the species. If you want to report a sighting, please include a photo of the pink egg masses for species confirmation and send an email to TISI Director, Ashley Morgan-Olvera (email@example.com). TISI is actively documenting the distribution of these snails in collaboration with TPWD and USGS-NAS.
Citizens can remove pink egg masses. This is done by scraping off the egg masses to allow them to fall into the water since inundated eggs will not hatch. However, only pink egg masses should be scraped or removed. TPWD also recommends you destroy the egg masses before drowning them in the water, to ensure none survive. This can be done by stepping on the egg masses.
Cowie RH. 2002. Apple snails (Ampullariidae) as agricultural pests: their biology, impacts and management. In: Barker GM, eds. Molluscs as crop pests. Wallingford (UK): CABI Publishing. p 145-192.
Hayes, K. A., R. H. Cowie, S. C. Thiengo and E. E. Strong. 2012. Comparing apples with apples: clarifying the identities of two highly invasive Neotropical Ampullariidae (Caenogastropoda). Zoological Journal of the Linnean Society. 166:723-763. https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1096-3642.2012.00867.x
Naylor, Rosamond. 1996. Invasions in agriculture: assessing the cost of the golden apple snail in Asia. Ambio 443-448.
U.S. Fish & Wildlife Service. Giant Applesnail (Pomacea maculata) Ecological Risk Screening Summary: https://www.fws.gov/fisheries/ANS/erss/highrisk/ERSS-Pomacea-maculata-FINAL-March2018.pdf
Teem, J. L., Y. Qvarnstrom, H. S. Bishop, A. J. da Silva, J. Carter, J. White-Mclean, and T. Smith. 2013. The occurrence of the rat lungworm, Angiostrongylus cantonensis, in nonindigenous snails in the Gulf of Mexico region of the United States. Hawai’i Journal of Medicine & Public Health 72(6 Suppl 2):11-14. Accessible here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3689474/
Teo, Su Sin. 2001. Evaluation of different duck varieties for the control of the golden apple snail (Pomacea canaliculata) in transplanted and direct seeded rice. Crop Protection 20(7):599-604.
Wada, T. 1997. Introduction of the apple snail Pomacea canaliculata and its impact on rice agriculture. In Proceedings of international workshop on biological invasions of ecosystems by pests and beneficial organisms, ed. National Institute of Agro-Environmental Sciences, Tsukuba, Japan, 170-180.
Yusa, Y. & Wada, T. 1999. Impact of the introduction of apple snail and their control in Japan. Naga, ICLARM Q 22(3):9-13.