Tuesday, March 11, 2008

Hey kids! The slugs are eating the garden!

Last night, putting out the trash, I nearly stepped on this character, a Great Grey Slug, Limax maximus, the first one of the year. I remembered a Far Side cartoon, a family staring out the window at a yard full of slugs, with the caption, “Hey kids! The slugs are back!” But in reality, the reappearance of L. maximus is one of the not-quite-so-welcome signs of spring. These guys do a lot of damage to garden plants.

I saw that Wanderin’ Weeta has also posted a slug, a smaller one that I believe is Deroceras reticulatum, the Grey Field Slug. In the spirit of general sluggishness, I have decided to post a modified entry from a previous, now defunct blog. To exaggerate novelty, I'm using green lettering.

The Good the Bad and the Slugly

Many of our commonest slugs, snails and other soil-dwelling invertebrates (worms, ants, and so on) are originally from other continents. The soils of the world are the true melting pot of the planet, because the eggs and other life stages of many small life forms have been transported inadvertently by humans far and wide for generations. And as is often the case, the imported species are problematical to the ecology of a region, by out-competing or preying upon natives that lack the evolutionary leg up to cope.

Banana Slug, local version.

Of our three largest slugs, only the Banana Slug, Ariolimax columbianus, is native. It is the second largest species in the world and can grow to more than 20 cm. If there is a creature that truly symbolizes the great rainy Pacific Northwest, I suggest it is the Banana Slug. It's a good slug, almost never found in gardens or crops. In natural habitats it acts as Nature's garbage collector and recycler, consuming and further breaking down dead and decaying matter. In Richmond, Banana slugs tend to be uniformly grey-green. Elsewhere in their range they can be banana-yellow, with overripe banana-black spots.

The conspicuous hole on the side of the slug is called the pneumostome. Air passes through here to the gill, a reminder that slugs have an aquatic history and are brave pioneers of the terrestrial world. There is only one pneumostome, on the right side, harking back to the shell-bearing ancestry of all slugs. Snails are not bilaterally symmetrical (left side = right side), thus neither are their slug descendants

European Great Grey Slug.

The Great Grey Slug of Europe, Limax maximus is a voracious garden pest, and the fastest of our slugs. It is able to crawl four times faster than the Banana Slug, perhaps 6 inches in a minute. Not only will it devour many species of plant, this slug is also a predator who will stalk and eat other slugs. I have not witnessed this, but have seen footage of cheetahs chasing gazelles. It is probably similar, but much slower.

European Black Slug, rhumba.

The third large species is the European Black Slug, Arion ater. It can also be grey or brown, has a furrowed back, and often has a rusty orange edge to its foot. It is another import known to attack crops and garden plants. (It loves strawberries.) If you encounter one and are feeling bold, poke it gently. It will tighten into a ball and start wobbling side to side, very slowly. It is one of nature's most inexplicable and strangely mesmerizing performances, worth watching if you have a lot of time to kill.

One thing that all slugs have in common is slime. They use it for protection and as a slick yet sticky surface that makes crawling that much easier - and speedier! At a molecular level, slime turns out to be a highly organized material that can absorb up to 100 times its original volume in water. This property is readily apparent should you ever make the mistake of trying to rinse slug slime from your fingers. Slime begets more slime. Simply wait for it to dry and then roll it off, as you would rubber cement.

As for ridding your garden of slugs in a safe, non-toxic way, you can get a duck, or one of these:

Slug trap.

Fill it with beer, the slugs enter, imbibe, and drown. Advantage: doesn’t require dangerous poisons. Disadvantage: doesn’t require something that isn’t beer.


BerryBird said...

Have you ever seen L. maximus mate? When I started seeing them on my back porch, I looked them up to see what they were, and discovered they are truly fascinating beasts. Unfortunately, I haven't been lucky enough to witness any romance.

Hugh said...

Yes, I've seen it, once. They were hanging from a leaning tree trunk in the nature reserve where I worked. Very slow motion Cirque de Soliel.

Follow the links from BerryBird's comment to see what we're talking about.