PHOTOS COURTESY OF ROBIN ROSETTA.
We’re in a race with snails and slugs, and we are losing. Wait, you say, aren’t these slimy denizens of debris doomed to a slow crawl? How can they win? Easy: We’re helping them.
Invasive slugs and snails are moving at a global pace. Snails and slugs are transported via several routes, particularly with local, regional and international trade of a diverse range of products such as cut flowers, vegetable and fruit imports, nursery stock and Christmas trees. They are inside and outside various cargo shipping containers and trucks, and they are moved via the pet trade and Internet sales. In my own landscape, I’ve tentatively identified nine exotic slugs and snails (and the brown garden snail a block away).
Snails and slugs are known as gastropods (Latin for “stomach-foot”) and well-named, for they really are predominantly a stomach on a moving foot. They are part of the phylum Mollusca, which includes octopi and oysters. Although snails and slugs are often reviled, we do savor some, which has led to the dispersal of delectable species throughout the world. An example is the European brown garden snail, Cornu aspersum, which has slithered from the plate to predicament as one of the most damaging snails in agriculture. For nurseries, this is the quarry leading to quarantine and the inevitable spray regime to eradicate them from the production site. But there are many other species of concern for which to watch.
A snail summit
In March of 2009, 37 university, regulatory, grower, consultant and agricultural chemical industry representatives met in Portland, Ore., to discuss issues related to snails and slugs in ornamental systems. The meeting was funded by the Western Region IPM Center (University of California-Davis), and the purpose was to communicate about the current status and economic impacts of these pests, discuss control efforts and identify research priorities.
The nation’s top malacologist (a scientist who studies mollusks), Dr. David Robinson of the USDA’s Animal and Plant Health Inspection Service, described the threat of several key species of snails and slugs. The vineyard snail, Cernuella virgata, has shown up adjacent to a major port and is currently under eradication. The wrinkled dune snail, Candidula intersecta, has also been detected in a former harbor and near railroad transportation. Increasingly found is the decollate snail, Rumina decollata, used as a snail biocontrol agent, but it is phytophagus itself and may harm native gastropod populations and cannot be shipped outside of limited areas. Amber snails (Succineidae) are found in increasing numbers throughout the United States in nursery production, sometimes leading to shipment rejections or destruction. Many are native species but difficult to distinguish from damaging, actionable species of concern.
Vigilance should also be maintained for the white garden snail, Theba pisana, the most frequently intercepted snail that is also established in Southern California and is causing significant damage there. Dr. Robert Hollingsworth, of the USDA’s Agricultural Research Service, adds orchid snail (Zonitoides arboreus) to the list of snails of concern due to its damage that affects the $22 million orchid crop in Hawai’i. Catherine Mannion, University of Florida, has noted that the Cuban land snail, Zachrysia provisoria, voraciously feeds on ornamentals in South Florida. And nearly everyone warns of the Giant African Snail, Achatina fulica, a battleship-sized snail (only a small exaggeration) that eats a wide range of economic crops. This particular creature also vectors the rat-lungworm parasite, Angiostrongylus cantonensis, which can cause potentially lethal eosinophilic meningitis. The disease is far worse than its pronunciation.
Spotted leopard slug
Slugs on the move
Among the slugs of concern, Sloan’s leatherleaf slug (Veronicella sloanii sloanii), may have been found in Florida. Many of the slugs, like the leatherleaf, are of tropical or semi-tropical origin and threaten agriculture and landscapes in the warm areas of the U.S. These include Bradybaena similaris, thought to be in California and currently in Gulf Coast states; Veronicella cubensis, currently found in Hawai’i; Meghimatium striatum, a Phylomycid slug in Hawai’i and California; the semi-slug Parmarion martensi, and the slug Pallifera sp., new finds in Hawai’i. Temperate states beware! The Spanish slug, Arion vulgaris has caused considerable damage in Northern Europe. I’m consistently sent images of the spotted leopard slug, Limax maximus, a daunting consumer of landscapes, from throughout the U.S. Its damage is only mitigated slightly by the entertainment value of its courtship, with two slugs dangling from a slime cord in an enthusiastic embrace while mating.
Dr. Kenneth Hays, Pacific Biosciences Research Center, University of Hawai’i-Manoa, researches introduction pathways for alien snails and slugs. His initial work consisted of a survey of 40 nurseries on six of the Hawaiian Islands. He found 31 species; including five new records for Hawai’i and 21 new island records. There were one to 17 distinct species at each nursery. He noted some species were more likely to be found outside of a greenhouse than inside and vice versa. For example, an unidentified Philomycid slug, Gulella bicolor, and Succinea costaricana were only found inside, while several species such as Arion sp., Limax maximus, Milax gagates and Oxychilus alliarius were only found outside.
What’s to be done?
One of the conclusions from the meeting was the need for more support for taxonomic/identification of snails and slugs. There is only one official identifier, Dr. David Robinson, whose main charge is identification of foreign gastropods. There currently is no formally assigned position that focuses on snails and slugs found domestically. Recently, more people have been trained to distinguish species using external and internal (genital structure) morphological characteristics, but these features are variable and are often limited to mature specimens.
Increasingly, identification utilizes molecular methods, exemplified by the work of Dr. Rory McDonnell, University of California-Riverside, who is using extracted DNA and restriction enzymes to match samples to genetic databases. McDonnell has also teamed up with Dr. Tim Paine and Dr. Mike Gormally (both at UC Riverside), to produce the very useful, Slugs: A Guide to the Invasive and Native Fauna of California, which can be downloaded for free at http://anrcatalog.ucdavis.edu/pdf/8336.pdf. There is currently collaboration between Oregon and Hawai’i to identify amber snail species in nursery production with Dr. Brenden Holland, University of Hawai’i, using DNA techniques to match samples with his growing database of Succineidae.
There is considerably more information that was gathered at the Snail and Slug meeting including current research, management practices and product updates. A summary of presentations is available at http://oregonstate.edu/dept/nurspest/WRIPMC_Snail__Slug_Meeting_Summary.pdf.
At the 2010 International World Snail Racing Championships, Sydney the Snail beat his competition by moving 13 inches in three minutes and 41 seconds. He would travel nearly 18 feet in an hour at that snail’s pace, but now he can hitch a ride on a jet and be anywhere in the world in hours.
Robin Rosetta is associate professor, Integrated Pest Management Extension at Oregon State University’s North Willamette Research and Extension Center, Aurora. She is editor of the Pacific Northwest Nursery IPM website, located at www.oregonstate.edu/dept/nurspest, and can be reached at Robin.Rosetta@oregonstate.edu.