The Oregon Caves forest snail (“Monadenia rothii”) only lives at or very near the Monument. The proverbial slowness of snails prevents genetic mutations from being diluted out of existence by interbreeding with large populations. When enough mutations and genetic drift add up, a new species is born, resulting in more snail species only found in our bioregion compared to nearly all other groups. Even relatively fast moving mollusks like banana slugs are confined to the Pacific Northwest. Butterflies, reptiles, and birds have no species confined to our region, largely because they move too fast.
The forest snails above Oregon Caves are nine times more often seen on calcite-rich marble than on non-marble rock. The marble snails grow our region’s largest shells by eating calcite scraped off marble and so are more easily spotted and/or die sooner than snails in calcium-poor areas. The relative lack of calcite rock in most of our region is one reason why most of our snails are so tiny and why slugs do so well here.
One way to cope with low calcium is to lose your shell. The mantles of taildroppers are vestiges of shells, like our appendix may be the shrunken remains of a cow-like stomach. Like certain mites, spiders and millipedes, taildroppers have different species in Asia and the Northwest, suggesting a warmer climate or lower sea level once connected both areas. When chased by certain beetles or snails, a ring of muscles contracts, causing the tail to drop off, hence the name. The slug may then change its odor and run away as fast as slugs can, leaving an attractive wiggling tail end behind, apparently with its original odor.
Slime is such a good lubricant that slugs slide over upended razors without injury. Since slime molecules change shape and fluidity, depending on how much pressure is applied, you can feel this change by pinching slime, pulling your fingers apart, and then sliding them sideways. This slime change allows mollusks to grab ground and pull forward with their “foot” and then slide downhill on now liquid slime. Long thin protein fibrils in the slime apparently coagulate under pressure, much like heating eggs. However, releasing pressure returns snail proteins to their original sliminess, something I have yet to do with eggs. When threatened, slugs make enough slime to be too slippery to catch. Unfortunately, this doesn’t work against beetles specialized in eating slugs.