Autumnal Slug Rain––another kind of rain

September 17, 2016

Friends of Willapa Refuge held a ‘Wonders of Willapa’ event at Tarlatt Unit today. The weather was wet, with steady rain during the morning and longer and longer breaks between rainy periods as the afternoon went on. We stopped by the site around 2 p.m., and walked out to the Tarlatt Slough viewpoint, where you can look north in clear weather to the Olympic Mountains. Not one peak was in sight today, low clouds obscured even the north bay. 

The view north along Tarlatt Slough:  Water and sky merge in the rain.

The highlight of the walk was multiple slug sightings. In some areas, there were slugs every three to five feet. Occasionally, there were three or more slugs within a couple of feet. 

Two Pacific Bananaslugs (lower left and upper center) and a Chocolate Slug (upper right).

I’ve walked in ancient forests in late February, in the rain, and stepped over a frog or salamander with ever step. We call these Salamander Rains, when the coldest temperatures of winter are easing into spring, the soil is thoroughly wet, the air is wet, and amphibians can easily move around from winter hideouts to spring mating streams and ponds. 

In late summer, after months of dry weather, the first soaking rains wet the ground, promote decay of drying vegetation, and voila! The slugs come out of their summer hideouts and frolic in the broad light of day, or so it seemed today. 

Low light, ample food (decaying leaves and fungi for Pacific Bananaslugs, introduced vegetation for Chocolate Slugs), and plenty of atmospheric moisture made this an ideal day for gliding and browsing by slugs, and while the calendar is not quite to Fall, it seems appropriate to name this an Autumnal Slug Rain––not a rain of slugs, but a rain that brings out the slugs. 

A buckskin Pacific Bananaslug, pale yellow and gliding over grasses on the dike.

Pacific Bananaslug, Ariolimax columbianus, is the largest native slug on the coast, commonly seen in forested areas. On the dike these slugs were many yards from the coastal forest, which is their usual habitat. Bananaslugs eat decaying vegetation, mosses and fungi.  The damp day and ample food lured more than one hundred bananaslugs out into the open for the first good noshing they’d had in wet daylight weather for many months. Coloration varied from pale yellow to ochre yellow, some with black spots (small to large), and others plain, or in local lingo, pinto, appaloosa and buckskin slugs. 

Another color form of Pacific Bananaslug, with black spots on an ochre brown body. 

Chocolate Slug, Arion rufus, is one of the larger introduced slugs in the Pacific Northwest. Colors vary from medium brown to very dark brown to black. Today we saw medium brown and very dark brown colorations. This slug is common in gardens, and rarely found in native forest. The dike is largely covered in introduced grasses and flowers, so it too was right at home, feeding in the open on a suitably wet afternoon. As with the bananaslugs, there were more than one hundred Chocolate Slugs in the short walk from the edge of the forest to the overlook area. 

Chocolate Slug, with a medium brown, milk-chocolate-colored body.

I did not see any native or introduced snails today. Shells provide them with some cover during dry seasons, allowing them to move a bit more freely than slugs can. 

Another Chocolate Slug, this one is more of a dark bitter chocolate brown color.

To read more about terrestrial mollusks, see the recent book, Land Snails and Slugs of the Pacific Northwest, by Thomas Burke, with photographs by William Leonard, OSU Press, 2013. There are dozens of native and introduced species in the coastal Pacific Northwest. As for rain terms, at last count, my rain words list has more than one hundred twenty terms.