When most snailologist (not really a word) mention the group of terrestrial snails known as the Amber snails (Family Succineidae) they usually temper the forthcoming description with something like…
“The taxonomy of the North American Succineidae is in need of studies using modern techniques to determine taxon validity and relationships.” This from John Burch, the master of North American freshwater and terrestrial snails for many years says,
Others manage similar conclusions:
“The taxonomy of this group is difficult with some recent workers suggesting that a number of sibling species may be present based on anatomical, shell, and habitat characteristics (Frest 1991). However, the plasticity of anatomy and convergence in shell appearance between races suggests that a more conservative approach be taken.” Jeffrey C. Nekola (Maine snail hunter)
No one comes quite far enough for my liking— this family is in a sorry state. In generally no one really has a clue about this group of snails. Here is my guess, most described “species” within this family are not true species. This includes some ‘species’ that, due to lack of apparent abundance, have made lists endangered or threatened species.
All this to say that during a walk down the road along the coast of Maine I encountered perhaps the most common land snails in the region, an amber snail. These are known to come out of the grass and crawl into the road (Nylander 1936). This is most likely the species Succinea ovalis but given the uncertainly that plagues this group, who really knows. For now that will be this species — maybe now and forever.
In 0.5 miles of road I counted 15 snails.
The next day, along the same stretch I counted only 6.
The next day, again along the same bit of road, I counted 14.
I also encountered a few snail smears, presumably what was left of road snails smashed into the tarmac. I expected more smears but this road is not busy and most snails appeared along the edge of the road within a few feet of the grassy edge.
A few feet from the road, into the foliage I find myself in a coastal forest. Here larger trees are pines, spruces, beech, and gray birch but the dominant tree, small and often tangled, is the Alder. After a rain its not the amber snails that appear here but a bright orange slug. This slug, which I remember from days exploring these woods as a child, is Limacus flavus — the Tawny Garden Slug. This is a non-indigenous species; but has been a part of this ecosystem for many years. These bright orange slugs easily stand out from a dense green background. They do not stand out quite so easily amongst the many colored stones, dead tree parts, and occasional mass of pine needles that litter this forest floor.
My obsession for counting came out when I spied my first slug and I began a tally while I walked an approximately 0.5 kilometer trail through the woods to the shoreline. The count, 39 slugs. How best to estimate the population in these woods — I’m walking in a 34 acre preserve. I decided to count the same slugs on my way back. Going back the same trail I again counted slugs, this time I also included any distinct trail characteristics. Then, once finished I reconciled my two list—one to the shore and one back— to determine if I missed any. This is a modification of the double-observer method (see Powell and Gale in the further reading section for more). This method, which usually has two separate observers, allows an estimate of the detection percentage. I found it quite amazing that I missed slugs, in both directions. This type of detection error is of course the reason for a method like this. A little quick math and I had a reasonable estimate of the slugs per 500 meters square (500 meters of walking plus a search area of 0.5 meters either side of my path). I repeated this count on other trails in the next several days. Average slug count, 35. If the density of slugs I saw were indicative of the whole preserve then between 7000—11,500, average of 9671, slugs are roaming that wooded coastline.
Further to the north but still along the Maine coast, In Acadia National Park, I have never observed the Tawny Garden Slug. Instead the (also) non-indigenous slug Limax maximus — the Great Gray Leopard Slug has been the slug I have noticed in past years. This summer (2018), however, I have yet to find a single one.
Reason for the absence: Warm weather? dry weather? It has been a warm and dry season but the rain still comes and, at times, the forest floor has been wet.
These Non-indigenous slugs (Limax maximus and Limacus flavus) have been here for years. What problems have they caused? Limacus flavus is an attacker of gardens. Will problems increase as climate warms? Will a warming climate knock them out? So many questions.
Another non-indigenous denizen of the coast is found further toward the water. The Common Periwinkle, delight of many shoreline walkers and tide-pool hunters on the rocky coastline. This snail, like the slugs, has been around for a long time—in the case of the periwinkles they have been on the Maine coast since at least the mid 1800s and we should probably just consider them native.
I was exploring some tide pools along a rocky headland in Acadia National Park and saw some young periwinkles (young Common Periwinkles not to be confused with the two other periwinkle species found nearby—the Rough Periwinkle and the Smooth Periwinkle, which share a genus with our non-indigenous friend, Littorina, but are smaller and more restricted in their habitat.) hiding out in the shell of dead barnacles. This probably helps them withstand the turbulent waves that come in on the tide’s return. It is also probably an effective anti-predator behavior. Crabs would have a hard time digging these winkles out. I wonder if these snails ever get stuck because they grew too large to escape within the protective confines of the barnacle shell, which are larger inside then the opening.
Next month I'm going to try to get away from snails -- try :-)
Some further reading, good luck finding Nylander’s work:
Nekola, J.C. 2008. Land Snail Ecology and Biogeography of Eastern Maine. Report Submitted to Maine Department of Inland Fisheries & Wildlife.
Nylander, O.O. 1936. Land and Fresh Water Shells of Aroostook County, Maine. Unpublished Manuscript NYW-0010 at the Nylander Museum, Caribou Maine.
Powell, L. A., and G. A. Gale. 2015. Estimation of Parameters for Animal Populations: a primer for the rest of us. Caught Napping Publications: Lincoln, NE.