A Most Curious Slug
Science in Action!
The white, two-story house looks like many others in the tony Seattle neighborhood of Laurelhurst: understated and elegant with a well taken care of yard. Few who walk by would guess that a notorious beast dwelt there until June 24, 1933, when California naturalist Tracey Storer caught it and took it south. Storer’s animal, a several-inch long slug, known scientifically as Arion rufus, now rests in ethanol at the California Academy of Sciences.
For those who inhabit Seattle, or nearly any city between Arcata, California, and Vancouver, BC, finding an Arion rufus in their yards would not prompt them to collect one, take it to a leading scientific institution, and preserve it for posterity. Most people would probably kill the slug on the spot, or, if they were feeling generous, they might scoop up the offending gastropod and transfer it out of their yards. The difference between now and then is that modern urbanites see Arion rufus—known to malacologists by the yummy dessert-sounding-name of chocolate Arion—as a slimy, good-for-nothing garden despoiler. Instead, Storer saw the slug as an unusual individual, singular in its appearance in Seattle; the one he collected is the first known specimen of this European native ever found in the western United States.
First discovered in this country in Detroit in 1912 and described as “a striking and beautiful object,” Arion rufus do not do well in cold climates. In contrast, the temperate, wet conditions of the PNW allowed the slugs to became a pest in Seattle by 1940, followed within a decade or so by Oregon, Vancouver, B.C., and California. University of Washington biologist Eugene Kozloff summed up many people’s feelings about Arion rufus when he wrote, “If you have to hate anything, let it be this slug, a cruelly destructive pest if there ever was one.” That seems a bit harsh to me; after all they are only eating your vegetables.
Plus, like all animals they have some rather nifty adaptations. When attacked they shrink into a ball, rock from side to side, and cover themselves in slime. Although the mucus gums up the mouth of most attackers and prevents them from getting a grip, it is useless against another non-native, the great gray slug. In this situation, A. rufus tries to speed away, hoping that the great gray attacks the slime puddle. If the attacker doesn’t fall for this stunt, the chocolate Arion is doomed; the speedy grays can quickly chase down a lumbering chocolate Arion. Those dead slugs you encounter on the pavement in the morning may be the result of slug-on-slug predation and not too much sun.
According to the splendid Land Snails and Slugs of the Pacific Northwest by Thomas E. Burke, at least 29 species of slugs occur in Washington. Many, including 12 invaders from Europe, inhabit urban areas. A dozen years ago, I was lucky enough to hold one of the most beautiful natives in my hand, the blue-gray taildropper. What made the experience exciting and memorable was that the slug lived up to their (they are hermaphrodites, so they seems appropriate) name. When I looked away and then back again, two slugs, or at least one slug and their recently autotomized tail, nestled on my palm. We also have seven species of jumping-slugs, some of which can become airborne. They accomplish this feat via twitching; sadly I haven’t seen this.
Not everyone, however, is so quick to rise up against slugs. Back in Seattle, after hearing about the infamous slug collected by Tracey Storer, the home’s owner, a gardener, told me, “I guess I will have to be kindler and gentler to them.”
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Did you know that our native kokanee (the non-anadromous form of sockeye) were recently rediscovered in Lake Washington? I was lucky to interview and write about the biologist who found them. Here’s the story.
November 8 - 7pm - I will be live and in person with my pal Lynda Mapes at Brick and Mortar Books. We’ll be talking about our books. It will fun. Come on by and support a fine local bookstore. (Last week I wrote that this would be virtual. Sorry to make that mistake.)