Slug Slime and Other Weirdness

If you’ve ever planted a garden in western Oregon, you’re acquainted with slugs, or at least their damage. Did you know these pests are invasive species? Nine out of the 10 species of pest slugs in Oregon are non-native.* Like a lot of other little invertebrates, they’ve hitchhiked around the world in soil, including potted plants.

If you have a hankering to find slugs, the best time to do so is early morning. They don’t like sun, which may explain why they thrive around here—especially when one considers the lack of sun we’ve experienced this spring . . .

I share my garden with several invasive species and the native hotdog-sized Pacific banana slug, Ariolimax columbianus. I’m on a first name basis with these guys. I call them all “Larry.”  Banana slugs are too big for me to kill without feeling bad, so I give them flying lessons every time I encounter one. They always seem to come back for more, so maybe they like it. Larry is a real Oregonian, and not generally considered a pest, but he sure likes my lettuce,and last year he nearly ate my precious giant pumpkin seedling before I spotted him chowing down from a second story window.

Larry and I have a hands-off relationship. His slime is amazing. It does not wash off—soap and water won’t touch it. A quick Internet search indicates scientists have noticed that banana slug slime sticks particularly well to skin, it might have antiseptic properties, and someday it could be useful as a biological glue.

If it weren’t for the slime, I might try Larry for dinner. Other people have eaten them.**  Oregon escargot anyone? Regular escargot comes from European brown garden snails, Helix aspersa, another garden invader. Brown garden snails are established along the Oregon coast and in numerous residential neighborhoods in our cities and towns. Every year, I find a few on the sidewalk near the my office. Their shells are fragile, so I suspect they graze the sidewalk for calcium, a much-needed nutrient that fortifies their shells and protects their soft innards.

As if encountering banana slugs in my garden and watching snails grazing on sidewalks isn’t weird enough, years ago I encountered a slug at eye-level dangling in mid-air from a tree branch. It gets weirder. Some slugs mate in mid-air! If you don’t believe me, check out this video: http://beestingbrose.blogspot.com/2009/08/elegant-slugs.html. Don’t try this at home!


Dan Hilburn

*http://oregonstate.edu/dept/nurspest/slugs.htm

**http://rickshawunschooling.blogspot.com/2007/10/wild-food-killing-our-own-meat.html

Invasive Species: Melting Pot or Natural Disaster?

Two very different articles on invasive species appeared in my email box recently. Mother Nature’s Melting Pot* encourages us to “embrace the impurity of our cosmopolitan natural world.” In contrast, Should Biological Invasions Be Managed as Natural Disasters?** promotes building “a culture of safety and resilience,” requiring a “national and international commitment to prevention, preparedness, and vulnerability reduction.”


A similar contrast is evident in two recent local events. The Oregon Invasive Spiecies Council (OISC) held a statewide summit on invasive species last fall to highlight the importance of invasive species issues in Oregon. A few months later, the Public Interest Environmental Law Conference (PIELC) held a conference on “Environmentalism Gone Awry: The war on invasive speces – the need for a rational assessment of the costs and benefits of invasive species control.” Clearly some people see invasive species as one of the worst environmental problems we face; while others wonder, What’s the big deal? They’re going to get here sooner or later anyway, so why should we fight it?

How can people see this issue so differently? The first problem is a matter of definition. Invasive species doubters point to all the beneficial plants and animals that are not native. It is true that most of the food we eat comes from non-native plants and animals. It is also true that the grass in our lawns and the plants in our yards are mostly not Oregon natives either. This argument is a red herring (not native?). I think we can agree that lots of exotic species are beneficial and integral to modern society. Going completely native is not possible in this day and age, nor is it desirable.

Second, it is easy to find examples of invasive species response programs that didn’t work. Perhaps the most famous was the attempt to eradicate imported fire ant, Solenopsis invicta, from the Southeast using Mirex. Rachael Carson’s book, Silent Spring, was published during this project, and shined a spotlight on the ecological dangers of wide-area use of persistant pesticides. Sudden oak death, Phytophthora ramorum, provides a less dramatic example from right here in Oregon. Starting in 2001, a consortium of state and federal agencies attempted to eradicate this disease from the forest just north of Brookings. It didn’t work, though we did dramatically slow down the spread of this invasive disease.

The arguments that invasive species are no big deal or not worth fighting fall away if you focus not on all non-native species but on the small percentage that are really pests or weeds – the real invasive species. Oregon statute (ORS 570.750 (2)) recognizes: “invasions by harmful nonnative species are damaging to the environment and cause economic hardship. . .” The key word is harmful. There are hundreds of non-native species in Oregon that don’t fit this definition. We’re not talking about those.

Secondly, you can’t talk about the failed programs while ignoring the successes. There are many, many examples of successful invasive species response programs that get very little recognition. It is easy to write a book or hold a conference about about the big in-your-face failures because the consequences are obvious. It is much harder to interest people in the success stories. Anyone for a conference on why we don’t have gypsy moths in Oregon? Would you buy a book entitled; “Kudzu, The Worst Weed That Doesn’t Occur Here”? Yet Oregon has a proud history of successful early detection and rapid response against gypsy moth, kudzu, and many other invasive species.

I suspect that there is another factor common to people that don’t believe invasive species are a serious problem. I’ll bet they don’t get out much and/or they wouldn’t know a native plant from an invasive weed if they tripped over one. Many people are pretty well divorced from nature these days. Do you know which of the birds at your feeder are native? Exotic? Invasive? Congratualtions if you do -- if you don’t, you should borrow a field guide from the library or Google a local bird list and learn the common birds (ditto for trees, wildflowers, butterflies, etc.). Knowing what you’re looking at adds a great deal to one’s appreciation of nature and makes it easy to understand the importance of keeping invasive species out of places where they don’t belong.

Dan Hilburn
*Raffles, H. 2011. Mother Nature’s Melting Pot. The New York Times op-ed April 3, 2011 on page WK12 of the New York edition.

**Ricciardi, A., M.E. Palmer, and N.D. Yan. 2011. Should Biological Invasions Be Managed as Natural Disasters?  BioScience. Vol. 61(4) 312-317.

Native Pests and Invasive Species

Periodically, ants invade my kitchen. They like our compost bucket and my multi-grain Cheerios. Like most entomologists, I have a relatively high tolerance for bugs, but I draw the line at ants in my cereal. The most common house ant in this area is the odorus house ant, Tapinoma sessile. These small black ants are attracted to moisture and sweets; that’s why they like kitchens. Interestingly, they are not an invasive species; odorus house ants are native. We invaded their territory, not the other way around.

In fact, most of the ants we have in Oregon are native, and thankfully most of them prefer outdoor living. There are exceptions, the pavement ant (Tetramorium caespitum), a recent introduction here, is another home invader. Argentine ant, Linepithema humile, and red imported fire ant, Solenopsis invicta, have also been collected in Oregon, though  the former has a very limited distribution and the latter is not known to be established. Both are well known invasive pests in other regions.

Another common Oregon house guest, the western boxelder bug, Leptocoris rubrolineatus, is a second example of a native insect that acts like an invasive species. Boxelder bugs invade homes in the fall. During spring, they appear again at windows trying to find their way outdoors. Except for being a nuisance, they are not harmful. In contrast, the brown marmorated stink bug, Halyomorpha  halys, does the same indoor/outdoor thing but is a serious pest of fruits and vegetables; it is a bonafied invasive species.

The world of weeds provides other examples. Western juniper, Juniperus occidentalis, can be quite invasive, but it’s homegrown. Salt cedar, Tamarix aphylla, has similar invasive tendencies, but is not from around here. Both can be aggressive invaders.

Early spring is the season where bedstraw (Galium) grows like gangbusters in my yard. It is coming on strong in my wildflowers meadow right now. I don’t like pulling it because it sticks like velcro to gloves. My wife get a rash when she handles it. Some bedstraws are native, others are not. One of these days I should get this particular species identified. To me it’s a weed, but it might be a common native known as cleavers or sticky willy, Galium aparine. I think it is easier for me to curse it, spray it, and pull it if I imagine it being an invasive species. No doubt that is why I haven’t bothered to bring in a sample. If that sticky nasty stuff turned out to be a native Oregon wildflower, I’d just cry—as I continue to curse it, spray it, and pull it . . . .

Dan Hilburn

Invasive Species Hopscotch

Years ago, the Oregon Department of Agriculture (ODA) responded to a call from a railroad company that reported a worker had been stung by ants. I went was sent to investigate. The train was stopped on a siding in Salem. One of the boxcars contained cotton seed destined for cattle feed. It took me only a few minutes to find red imported fire ants (RIFA), Solenopsis invicta, in the cargo. There were a lot of them. The boxcar was sealed up and fumigated.

RIFA is one of the old-guard invasive species in this country. Native to South America, these ants were introduced to Mobile, Alabama in the 1930s. They have since spread throughout the entire southeastern United States, and in the 1990s, they made the hop to southern California. As their name suggests, fire ants have a powerful sting -- it is painful to humans and fatal to baby birds and newborn animals. The mounds they build interfere with machinery. RIFA is old news in the Southeast, but it is back in the scientific spotlight.

Scott Bauer, a U.S. Department of Agriculture researcher, has been studying the genetics of RIFA. He and his collaborators collected ants from 2,144 RIFA colonies in 11 countries, including newly invaded sites in the Caribbean, Australia, New Zealand, Taiwan, and China. Genetic analysis indicates these new invasions are coming from the United States, not RIFA’s homeland in South America.*

Nik Grunwald at Oregon State University is uncovering a similar hopscotch pattern of spread by sudden oak death (SOD), Phytophthora ramorum. There are three clonal lineages of SOD in North America. One was introduced into California. Another first appeared in British Columbia or Washington, and a third hopscotched here from Europe. Amazingly, scientists haven’t yet found this pathogen’s native range!  It must be pretty inconspicuous at home.

Another invasive species playing hopscotch is the granulate ambrosia beetle, Xylosandrus crassiusculus. Home for this wood borer is Africa and Asia, but it invaded the southeastern United States in the 1970s. In 2004, we caught a bunch of them in The Dalles. They weren’t coming from Africa or Asia; they were hitchhiking in green railroad ties imported from the Southeast. It took us a couple of years to eradicate them.

Secondary invasions may be more important than we realize. Populations of invasive species are often much higher in invaded territories outside their native range and those populations may be pre-adapted for playing invasive species hopscotch.

*Science News. March 26, 2011. Vol. 179(7) pg. 15.

Dan Hilburn