AFGHAN ARABIA WILD
ARTICLES AND POSTS
LET’S TALK ABOUT SLUGS
John M. Regan
It is just about impossible to live anywhere near the coastal regions of the Pacific Northwest and not be familiar with slugs. Walk out on any of our damp cool mornings or evenings or anytime in between and their shimmering slime trails crisscross the sidewalk like lines on a roadmap. It doesn’t require much effort to find the source of the slime, either. Look down and there it is: a slow moving slick and shiny globular creature moving at a pace so slow you have to wonder how it gets anywhere at all.
Depending on your point of view slugs are either fascinating or disgusting; most people falling into the latter category. But no one harbors more enmity toward slugs than gardeners, and not without cause either. Ask anyone who has dreamed of chowing down on fresh produce grown in their own backyard and they will immediately regal you with the exasperating appetites of these voracious pests. And the biological vandalism does not stop at the backyard either. Damage caused by slugs is responsible for a large amount of crop loss. Just about every agricultural product grown is vulnerable to their ceaseless appetite and they will eat just about anything. Not all slugs, however, are delinquent eating machines. There are predator species that kill and eat other slugs and snails; and among the plant eaters there is some variation of appetites.
Of the three primary species in the Northwest it is a European import that causes the most destruction. The European Garden Slug comes in a number of color varieties. If you are a garden enthusiasts this is the slug you are probably most familiar with. Five to six inches long this slug is normally a rich dark brown or deep velvety black. Accidently introduced from the old country many years ago these slugs quickly made themselves a home and spread around the country almost as fast as the European Sparrow. Too bad they’re not as pretty.
The most common slugs of the Pacific Northwest coastal regions. From left to right: the Banana Slug, the European Slug, and the Leopard Slug. The European slug in the photo shows a red color, but they are normally a deep brown or black. On the far right is an unknown slug of some type, most likely another European import.
Next up on the crop damage watch is a smaller slug called the Leopard Slug. This guy has earned his name, not surprisingly, for the pattern of irregular spots that decorate its back. If you can get past the fact that the creature is a slug they do have an certain beauty.
Our most famous, but least destructive, is the Banana Slug. Named for its banana like dimensions when full grown, these slugs possess distinct features that make them instantly recognizable. Pale green to dull yellow with mottled black markings and a distinct “head” banana slugs are hard to miss. There are reports of foot long specimens, but most top out at the seven inch range. Just the same, that is a pretty healthy size for a slug. You will most likely encounter banana slugs in damp forest where they prefer to feed on fungi instead of your tender lettuce.
While earthworms dominate the underground in astounding numbers it is the slugs who take that title above ground. They are extraordinarily prolific breeders and we had inadvertently aided them. See those beautiful decorative rocks that surround your garden? See that impressive retaining wall you built with help from Home Depot? Take a peak under all this granite and concrete and you’ll see untold numbers of slugs and slug eggs all resting comfortably in the home you made for them. As if that weren’t enough we make sure that by constantly watering our lawns we keep things ideally cool and damp. No wonder they like us so much.
Slugs, as you have likely surmised already, are simply snails without shells. They are just one of the 50,000 species of animals that make up the phylum Mollusca which includes clams, oysters, squids, octopus, and snails. Narrowing it down from there slugs belong to the largest and most widespread class of mollusks called Gastropods. Gastropods, too, contain a huge number of species to include sea slugs, nudibranchs, limpets, and abalones. Our Pacific Northwest slugs and snails are grouped together as terrestrial gastropods.
The opening to the lung of the Banana slug on the left is
obvious. On the right is a photograph of a pair of slugs mating.
Note the very distinct sex organs possessed by both animals.
The opening to the lung of the Banana slug on the left is obvious. On the right is a photograph of a pair of slugs mating. Note the very distinct sex organs possessed by both animals.
All three of our common slug species are Pulmonates, that is, they breathe air through a lung instead of a gill. The opening to the lung of a slug is quite obvious when the animal is viewed closely. Another characteristic of hermaphroditism. Most slugs possess both male and female reproductive organs and as a result they are prolific breeders. Yet for so simple an animal mating is, in fact, a relatively complex affair. There is an actual courtship replete with body stroking and slug like “caresses.” Once courtship concludes each slug, true to its hermaphroditic physiology, inserts sperm into its partner. Banana slugs are (in some circles) well known for their very noticeable penis - which is often actually eaten by its partner after mating!
But what about that slime trail? Well, that is produced by a large pedal gland in the “foot.” Terrestrial pulmonates moved forward by contracting muscular waves that propel the creature over the mucous produced by the pedal gland. Although the actual foot of the slug is hidden underneath its body, these muscular waves are quite visible on the mantle that covers the foot. The contractions may move front to rear or rear to front depending on the species.
At the tip of each of a slug’s tentacle is a tiny dark spot. These are the animal’s eyes. Although these organs actually possess a lens and optic nerve the eyes are primitive and apparently serve only as light detectors. The primary sense organs of the slug are its tentacles. Many species have an upper pair and a lower pair of tentacles, the larger of the two on top. The tentacles are actually chemoreceptors that provide a surprisingly good sense of smell. In predator species these organs are especially well developed.
Slugs are not everyone’s idea of a cuddly pet, of course, but they do provide some fascinating observation for the budding naturalist. Mating behavior, color, waving tentacles, and locomotion are easily observed and photographed. And a high speed camera is not required.
AFGHAN ARABIA WILD
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