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17/09/2014 - Conquering the World at a Snail’s Pace

Görlitz, 09/17/2014. Scientists at the Senckenberg Research Institute in Görlitz have studied the expansion of the invasive Mediterranean Tramp Slug. This mollusk already inhabits large parts of Europe and Australia as well as North and South America. Among others, it was recorded for the first time in Mexico, Costa Rica and Ecuador. Regionally, this species can be a serious agricultural pest; however, it appears to reach its distributional limits in extremely cold or hot areas. In their study, which was recently published in the scientific journal “NeoBiota,” the researchers from Senckenberg also identify potential additional invasion countries for this slug.

A slug conquers the world: Deroceras invadens © Hutchinson
A slug conquers the world:
Deroceras invadens © Hutchinson

It arrived in West Germany in 1977, presumably as a stowaway with vegetable shipments from Italy, and it was first reported from the new Federal States one year after the fall of the Berlin Wall – the Mediterranean Tramp Slug Deroceras invadens. As the name implies - invadere is Latin and means “to invade” – this slug has a habit of settling in new areas.

“By now, this species of slug can be encountered almost worldwide,” explains Dr. Heike Reise, curator at the malacology section of the Senckenberg Museum of Natural History in Görlitz, and she adds, “It is primarily found in gardens or under scattered debris, but also in greenhouses and out in the open nature. They are brought in with imported vegetables, garden supplies or tiles.”

Together with her colleague from Görlitz, Dr. John M. C. Hutchinson, and a colleague from the United States Department of Agriculture (USDA-APHIS), the scientist has studied the distribution of these mollusks, which reach a length of about 3 centimeters. “We tried to determine in which countries the slug has already been established, when it first occurred there, and whether its expansion is correlated to specific climate factors,” explains Hutchinson, the paper’s lead author. To this end, the scientists evaluated the available literature, examined material from museums and other institutes and single-handedly collected specimens.

This species of slug is introduced through imports. © Hutchinson
This species of slug is introduced
through imports. © Hutchinson

Originally, this slug is native to the Mediterranean region. The first evidence of immigration came from the British Isles in 1930, and within 10 years, the land slug expanded to Denmark, California, Australia and New Zealand. “Today, Deroceras invadens  is found across large parts of Europe, Australia, North and South America, and the slug has also made itself at home on several islands, such as the Azores, Madeira and the Canaries,” explains Reise. In the context of the study, which was funded by the Paul Ungerer Foundation, the team of scientists could also document several first-time occurrences, e.g., in Mexico, Costa Rica and Ecuador.

“So far, the species has given Asia and Eastern Europe a wide berth,” says Hutchinson, and he adds, “We assume that the cold winters in the eastern countries and the hot, dry climate in central Spain and parts of Australia, Africa and Asia hamper the spread of the slugs.” However, they do not necessarily render it impossible; in Breslau, a population of these slugs survived several winters at temperatures as low as minus 22 degrees Celsius. In North America and Egypt, the slugs take advantage of the extensive agricultural irrigation systems. “These new habitats created by humans open new paths for the expansion of the slugs into areas that are normally inhospitable for animals, and they may serve as potential corridors for the settling of suitable, isolated habitats,” explains Reise.   

This invasive slug feels particularly at home in gardens and under debris. © Wolfgang Junius/Senckenberg Görlitz
This invasive slug feels particularly at home
in gardens and under debris.
© Wolfgang Junius/Senckenberg Görlitz

The scientists from Görlitz assume that the small slugs will continue to expand to other countries and regions. A comparison of the distribution pattern with climate data allows prognoses regarding potential new occurrences. ”In principle, all areas with a temperate climate can serve as potential habitat for these animals,” says Hutchinson, and offers the following recommendation: “In large parts of China and Japan, as well as in the southern U.S., it would be beneficial to pay close attention to this potential new immigrant. In some areas, early recognition and rapidly applied counter measures may possibly prevent the establishment of this slug.”

Dr. Heike Reise
Senckenberg Museum für Naturkunde Görlitz
Phone 03581 - 47605410

Dr. John M.C. Hutchinson
Senckenberg Museum für Naturkunde Görlitz
Phone 03581 - 47605410

Judith Jördens
Press Office
Senckenberg Gesellschaft für Naturforschung
Phone  069- 7542 1434

Hutchinson J, Reise H, Robinson D (2014) A biography of an invasive terrestrial slug: the spread, distribution and habitat of Deroceras invadens. NeoBiota 23: 17-64.
doi: 10.3897/neobiota.23.7745

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To study and understand nature with its limitless diversity of living creatures and to preserve and manage it in a sustainable fashion as the basis of life for future generations – this has been the goal of the Senckenberg Nature Research Society (Senckenberg Gesellschaft für Naturforschung) for almost 200 years. This integrative “geobiodiversity research” and the dissemination of research and science are among Senckenberg’s main tasks. The nature museums in Frankfurt, Görlitz and Dresden display the diversity of life and the earth’s development over millions of years. The Senckenberg Nature Research Society is a member of the Leibniz Association. The Senckenberg Nature Museum in Frankfurt am Main is supported by the City of Frankfurt am Main as well as numerous other partners. Additional information can be found at www.senckenberg.de.

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