Sometimes when you least expect it you find something that is a little bit different. Such was the case during a recent guided walk on the South Beach Trail in Pacific Rim National Park Reserve. Usually I expect to find Banana Slugs (Ariolimax columbianus) on this trail and they were out in huge numbers, probably in response to the recent rainfall. Occasionally, I’ll find a Chocolate Arion (Arion rufus), an introduced European slug that I like to call the Licorice Slug since its typical colouration and texture is like black licorice (the colour of this species varies from black through to a reddish brown). Finding two slugs in the early part of the walk was a bonus and maybe foreshadowed what was to come.
I know that the Yellow-bordered Taildropper (Prophysaon foliolatum) occurs on the west coast of Vancouver Island and have seen it several times in Uclulet so I was fairly confident that I’d run into one this year. They definitely don’t seem to be as common as the ubiquitous Banana Slug, the signature species of coastal temperate rainforest, but they’re worth looking out for. While I didn’t spot any on the way out to South Beach I noticed what I initially thought were two on the way back. Both were on old wet boardwalk and on other occasions I’ve seen them on wooden structures like decks and railings.
The Yellow-bordered Taildropper is a distinctive looking slug. It is yellowish or brownish grey in colour with a fine web of lines on the main part of the body (reticulation). Most noticeable is the yellow border and black stripes on the mantle. The fringe of the foot of this slug is greyish in colour and marked by dark vertical lines. When attacked by a predator, the tail of the Taildropper swells and its body in front of the groove of self-amputation contracts, severing its tail and releasing a large amount of very sticky mucus. Theoretically, the predator is discouraged by the mucus and focuses its attention on the less sticky tail remnant as the slug makes its speedy escape. Taildroppers can grow to 100mm in length though they can be much smaller. Look for these slugs in wet, coastal temperate rainforest. They’re often found in woody debris and in association with vegetation like Skunk Cabbage and Devil’s Club; the former is common along the wet boardwalk on the South Beach Trail.
At first I thought that the smaller of these two slugs was simply an immature Yellow-bordered Taildropper. With a little research and some deliberation, I now think that the smaller one might actually be a Reticulate Taildropper (Prophysaon andersonii). This species is smaller than A. foliolatum and pale brownish in colour. It also has a diamond mesh pattern on its back and the mantle is marked with dark bands but no yellow margin. The foot fringe is a pale gray and usually lacks vertical lines – these lines are lacking in the smaller slug that I photographed. This species is generally smaller, reaching a size of 60mm. Unfortunately, I didn’t turn both slugs over – P. andersonii has a brilliant white sole while P. foliolatum has a cream coloured sole. I’ll have to wait for Rob Forsyth, author of Land Snails of British Columbia to get back to me before confirming the identification. I’ll update this post when I find out more!
It’s remarkable what you start to notice when you pay a little attention to your surroundings! Fabulous that a casual walk in the woods would produce three, and possibly four, species of slugs on a wet west coast day in British Columbia.