Slugs, from the ground up A truce in a back-yard slugfest gives a gardener a new appreciation for the much-loathed Limax maximus.; OBSERVATIONS

When I slip, just slightly, in the dark,

I know it isn't a wet leaf,


But you, loose toe from the old life,

The cold slime come into being. ...


Even the caterpillar I can love, and the various vermin.

But as for you, most odious -

Would Blake call you holy?

-- Theodore Roethke In the beam of the flashlight, they made a ghastly tableau - slugs, scores of them, the gelatinous progeny of a rainy spring. Now they were consuming my vegetable garden in a slow-motion feeding frenzy, like some miniature species of vegetarian sharks.

The peas were past saving, just the shoots of vines with ragged shreds remaining. Slugs were chewing holes in the early leaves of cucumber plants, zucchini, even hot pepper plants.

They were eating the habanero plant, for God's sake - a 3-inch, black-striped monster beginning to climb the stem, tentative tentacles testing the air; a half-dozen tiny beige ones feasting on the underside of the leaves. I plucked them off and drowned them without mercy.

All this occurred in late May - before I called Bell Laboratories and found out how a slug is smarter than a Pentium II computer, how slugs helped Alan Gelperin patent an electronic nose.

But I'm getting ahead of myself.


Slugs seem to bring out the inner big-game hunter in that ordinarily peaceable human sub-species, the gardener. Skipping around the Internet in search of slug solutions, I was amazed at the brutal remedies proposed.

A Washington-state writer concluded one screed with the assuring words: "Cutting and stabbing also work well." Another gardening maven cheerfully proposed: "Keep barbecue skewers stuck in the garden at random. Your weapon is at hand to impale them!" Spray them with vinegar! others advised. Spray them with alcohol!

For prevention, there was no end to suggestions for sure-fire slug barriers: dryer lint; dog hair; human hair; powdered ginger; wood ash; talcum powder; seaweed; oak leaves; coffee grounds; sand; oat bran; Epsom salts; ground pecan shells; sprigs of rosemary; countless commercial concoctions.

I decided to confine myself to traditional traps of watered-down beer, which soon filled with the corpses of slugs that presumably died, if not happy, then at least in a drunken stupor. But all this slugging it out in the garden piqued my interest in the enemy. A call to the U.S. Department of Agriculture, though, turned up only confusion about just what a slug is. (A worm? A snail?) I was passed from office to office without finding an expert.

Eventually, from the Internet, encyclopedias and a few books, I managed to collect some basic slug facts:

* A slug is a mollusk, like snails, octopuses and most seashell occupants. It's a gastropod, literally "belly-footed."


* There are some 40 slug species, with life spans in the wild of a year or two. If my math is right, they take at least a week to travel a mile, sliding along on a trail of slime they generate from within. They are hermaphrodites, having both male and female sex organs, but for complicated reasons it still takes two to tango; one species mates in an astonishing, hourlong, midair ritual, dangling from a foot-long strand of mucus.

* Slugs can consume several times their body weight in a single night, rasping leaves using a file-like organ bearing several thousand tiny teeth. A single acre of farmland can contain a quarter-million slugs, and some species winter over by "estivating" - digging down below the frost line and entering a hibernation-like state.

An impressive resume for a mere mollusk. But who would have suspected a slug of having brains? Not I, until my hunt for a slug expert led to Alan Gelperin, a neuroscience Ph.D. at Bell Laboratories in Murray Hill, N.J., the research and development division of Lucent Technologies.

For more than 20 years, Gelperin has studied my garden nemesis: Limax maximus, the great gray slug, a European species that evidently reached the United States aboard plants imported around the turn of the century. Of all things, it was the slug's brain that drew Gelperin's attention. By studying how a slug learns, Gelperin, a "computational neurobiologist," tries to understand neural circuitry that might be replicated in a microchip.

"The goal is to find the algorithms, or computational principles, that a brain uses," he says.

The slug brain has long been a favorite for neuroscientists because of its relatively few, large neurons - and the fact that they keep functioning after being removed from the body. Gelperin estimates that the slug brain has perhaps 220,000 neurons (compared to about 10 billion in the human brain) of which 200,000 relate to olfaction, the sense of smell.


A slug has eyes on its long, optical tentacles, but they can't see much and are chiefly useful for detecting the length of daylight. Their brain contains a circadian clock that allows the nocturnal species to know when darkness has fallen outside and to begin its slow route home well before sunrise.

The noses, located on the same tentacles, are far more important to the slug in finding food and mates. In sniffing for pheromones, "They probably can detect as little as a few hundred molecules from 10 meters away," Gelperin says.

Back when NCR Corp. and Bell Laboratories were both part of AT&T;, Gelperin, drawing in part on his slug studies, designed and patented an "electronic nose" that could be used in grocery stores as a produce scanner. The laboratory model, which has never been commercialized, not only could keep from mixing apples and oranges - it could distinguish MacIntosh apples from Romes or Valencia oranges from navels.

Gelperin's slug experiments began in the 1970s with studies of "food aversion," in which, say, a slug is offered a desirable food, such as potato. Then, just as he digs in, he's subjected to something unpleasant - forced to breathe carbon dioxide or to taste bitter quinine.

After just one such experience, the slug will avoid potatoes for weeks, Gelperin found. Since then, he has conducted steadily more complex learning experiments, and discovered that in some respects, slugs' performance matches that of "rats, pigeons and undergraduates, the canonical subjects" of psychology experiments on learning, he says.

Some of the slug's feats of memory and logic cannot be matched by even a powerful PC, he says. "Multiplying 12-digit numbers, the Pentium can beat the slug," Gelperin says. "But in terms of pattern recognition - which is what recognizing odors is - and higher-order learning, what slugs do is beyond the computers of today."


Inevitably, Gelperin has developed a scientist's admiration for his subjects.

"This is one of God's creatures that's gotten a bad rap," he says. The slug, he says, is "a really quite complicated and marvelous little machine."

As for me, I have abandoned my beer traps in favor of pitching the slugs over the fence and far down the alley. Even with their mysterious guidance systems, their neural clocks and their Pentium-beating brains, I'm hoping that by the time they slime their way back to my vegetable patch, the harvest will be in.

Pub Date: 7/19/98