Of Slugs in Winter

Eight years after retiring, I still have a collection of potted plants that I used as examples when I taught botany. Through the summer months they reside under a tree in the back yard; I water them occasionally in dry weather, but in all other respects they are on their own. They grow with weed-like exuberance, but that is an illusion; they have lived in captivity too long and have become too soft to survive a Maryland winter. So each year I have to begin watching the weather forecasts in mid-October. Fall may come on a specified day according to the calendar, but biologists know it really comes according to the thermometer. We may have a few weeks when we can enjoy mellow days of bright red, yellow and gold colors in the fields and forests, but inevitably there comes a night when things change. The first killing frost arrives, and nature performs the alchemist's trick in reverse; the gold in the fields turns to lead, colors go to gray, and anything that hasn't got ready for winter is in serious trouble.

Some years this involves a last-minute rush, carrying plants in after dark to beat an unexpected cold snap, but this year I had time to do it right. I took a couple of days to clean the greenhouse, and then started bringing the plants in, re-potting and pruning those that needed it in the process. It was an enjoyable task. Some of them date back as far as the 1960s, and were given to me by friends who have long since died but were remembered that day. Some needed to be divided, providing extras to be shared with friends; a few had to be discarded. And one provided a surprise.

One plant had fallen over and rolled under its bench, and in that damp, dark environment, it had succumbed to decay. Fortunately, it was a duplicate, so it was no great loss. But along with its rotting remains in the half-spilled clay pot there was a mass of small, glass-like spheres. They were a little less than an eighth of an inch in diameter, and appeared to contain a clear, oily substance; and each one contained a tiny gray spot in the center, visible through a magnifying lens. Obviously they were eggs of some sort, and I could not recall seeing anything exactly like them before. But it was easy to guess where they came from; when I picked up the pot a large slug was curled up on the bottom of it.

Slugs are fairly common around here; some years they are rare, and at other times they become abundant enough to do damage to tomatoes and other vegetables in gardens. Most people know only that they are closely related to snails, and consider them repulsive because of the slime they produce. Not surprisingly, I find them fascinating.

The word, "slugge," seems to have been brought to England by the Vikings; it was incorporated into the Middle English tongue to mean someone who was slow in thought and movement, and remains in our modern vocabulary as "sluggard." It is not a bad description for the animals we now call slugs; they are never in a hurry, and, like Winnie the Pooh, are of little brain. I don't recall seeing them as a child; I first encountered them in my college zoology class, where I learned they were classified as Mollusks. This is a very large group of animals, second only to the insects in the number of species it contains; it includes snails, clams, oysters, squids, octopi, and several others you will never hear of unless you become a marine biologist.

Over 2,000 years ago, Greek biologists described slugs as "gastropods," animals that used their stomachs as a foot to crawl on. This is not literally true; their stomach is used for digestion, and is located inside the body where it belongs. The underside of the body, or "foot," is actually a muscle that produces wave-like contractions to move the body along. Slugs secrete a slimy mucous which holds them fast to the surface they are crawling on; it also to keep their skin from drying out. The mucous produced in some species is toxic; one species found on the west coast is said to produce a rash comparable to poison ivy. The ones we have around here are not toxic; the slime is supposed to taste bad, and may protect them from some predators. I've never tried them myself, but apparently they taste good to starlings. One of the oddest things I have ever seen was a starling that apparently had some sort of misdirected maternal complex, and tried to sneak into a blue jay's nest and feed slugs to the nestlings. The nest was just outside the window of our old house, and I watched the starling for a couple of hours. She would wait until the adult jays were gone and dart in to stuff slugs into the mouths of the chicks. The young jays didn't appear to like the slugs, and usually spit them out as soon as the starling was gone, but she persisted until the adult jays chased her away.

The reproductive process is the most bizarre thing about slugs. The common ones around here usually live only one year. They begin life as males, but by middle age they have become hermaphrodites, growing a set of female organs as well. The male organ is usually broken off during mating, so they end their lives as females. Toward the end of summer or early fall, they produce a few dozen eggs; these are usually buried in moist ground and remain dormant until spring. And that, I assume, was how the eggs got into my flower pot: in the dark, damp area under the bench, the slug didn't know the difference between potting soil and the soft loam of a forest floor.

I covered the eggs with damp leaves and left them where I found them. Chances are that they will freeze this winter, or some critter will find them and eat them; but that could have happened to them if they had been properly deposited in the ground. It was about three weeks ago when I found them; as of today, they are still there and look viable. It will be interesting to see how they fare as winter comes and goes… as it will for all of us.