Monday, December 1, 2008

Slimy snails, slippery slugs--more here than you ever thought

Something nipping at your seedlings and chewing at your leaves?

Could be a snail or a slug, and it could be because there are more of them here than anyone guessed.

(Image: Giant African snails, from the U.S. Department of Agriculture website,

A new survey found 38 non-native snails and slugs in nurseries in Hawai'i, five of them entirely new. They found two more species, but those were the native ones.

The surprising finding lands on top of the rejection of a Christmas tree shipments this year due to slug infestations. And it points to another way for alien pests to enter the Hawaiian environment. They can ride the winds and waves, hitchhike on planes and ships, but a lot of them arrive on plants.

If they arrive on aircraft, then they have a convenience denied to many human passengers these days: inflight meals.

The new study was published in the international Journal of Pest Management under the title, “The horticultural industry as a vector of alien snails and slugs: widespread invasions in Hawaii.” The authors are Robert H. Cowie, Kenneth A. Hayes, Chuong T. Tran and Wallace M. Meyer III, are from the University of Hawai'i's Center for Conservation Research and Training.

The infestation of nursery stock is a problem for various reasons. It can cost the nursery companies money when their shipments are rejected at the port. And they cause problems with production within the nurseries as they feed. Furthermore, they can cause problems outside the nurseries.

“When they are transported to and become established in new areas they may cause agricultural, horticultural and environmental problems,” the authors wrote.

The tiny coqui frog is an example. Unlike the snails and slugs, this denizen of nursery products makes its presence heard with a piercing evening call by its males.

The slug and snail study looked at 40 nurseries on six islands. Every nursery on every island was infested with multiple species.

“The rate of introduction of new species of snails and slugs shows no sign of declining,” the authors wrote.

They urge awareness on the part of nursery operators and quarantine officials. Nurseries, both to protect their own investments and to protect the gardens of their customers, are encouraged to maintain hygienic facilities.

In part, the issues is that with many of the smaller and hard-to-find species, it's not yet clear what their impacts will be on the local environment. Do they carry disease, do they eat some garden species in preference to others, do they compete with and push out native species?

“While some ... consequences, notably of the larger, more obvious species, are clear and dramatic, little is known about the impacts of the smaller and less noticeable species, yet these may also be important,” the authors wrote.

©2008 Jan TenBruggencate

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