Slugs

As promised--the enigma of the slug. As you probably know, this post was started in Seattle, when myself and the other NOSB-ers first stumbled across a three-inch long slug trying to cross a path at the Nisqually wildlife refuge. As is the nature of nerd-kind, we stopped to look, named him Matt, and fell to wondering why there was a gaping hole in his side that looked as if it had been pecked there by a bird.
Now we find out.
As is always best, I've found, I've decided to start with some background on the slug. For starters, they hail from the taxonomic phylum Mollusca, which includes a lot of the "weirder" species of earth such as cuttlefish and oysters. It's an old group of animals; we suspect they first became a distinct group around the Precambrian (600 to 4600 million years ago), and they have since built and diversified to a rough estimate of 200,000 described species. Slugs, specifically, are of the class Gastropoda, which translates to "stomach foot" in Latin. The name was earned in reference to the slug's apparent tendency to crawl around on its belly. In light of that, the muscular underside that they use for locomotion has been dubbed the "foot". Looking closely, one will note that a slug moves itself along by rippling the muscles along its underside in a wavelike pattern, lubricating its way with the famed snail slime (a stress-fracture fluid much like soap). The slime also serves as protection against drying out and sharp obstacles, and works so well that a slug could crawl over a razor blade without harming itself.

European black slug (Matt)

On the Seattle Adventure, we encountered three distinct species of slug. I am not the best at identifying gastropods, so the conclusions herein are hesitant; Matt and the other blackish-brown specimens that we encountered mostly in Nisqually were European black slugs (Arion ater) from the subfamily Arionidae. The reddish-tan ones were also from Arionidae (I could not pinpoint the species), and the leopard-spotted one from the rainforest was a banana slug (Ariolimax columbianus) from the subfamily Ariolimacinae. We noticed and wondered about on each of them the little hole that you'll note on the photo of the tan Arioninae specimen; they all had one, and they were capable of closing it and opening it like a sphincter. Research reveals it to be a "respiratory pore". Like our trachea, its purpose is to bring oxygen in from the environment, and it leads directly to the slug's single lung. In addition, the slug can absorb oxygen directly from the atmosphere, sucking it in through its porous skin and redistributing it throughout the body. Most of the organs are located on the dorsal side of the body to better allow the animal to crawl.

Unidentified Subfamily Arionidae

Now, as boneless, exoskeleton-less, shell-less animals with a record speed of around .013 m/s, one would pretty much suspect to see all slugs at the bottom of the faunal food chain. For the most part, that's true; slugs serve as the garbage disposal system of nature, breaking down dead plant and animal matter and recycling it back into the soil. They use their rasp-like "radula"--a ridged tongue that moves like a conveyor belt around a base of cartilage--to rasp away food particles and move it backwards down the gullet. They are hunted in turn by anything from birds to frogs, and for the most part eat at the bottom of the food chain.

Banana slug

There are exceptions to the rule, of course. Poiretia cornea, or the dalmatian slug, is carnivorous and, moreover, cannibalistic. It hunts other, smaller gastropods (specifically snails), chasing them down and then using the acids secreting in its slime to dissolve the shells of its prey. Some carnivorous species, such as the wolf snail (Euglandia rosea), have made a pest of themselves. The wolf snails were introduced to the French Polynesian islands to control a different species: the giant African land snails. Predictably, this did not work, and the wolf snails instead set about eating the smaller, native species and driving most of them extinct.
To finish off the post, I'll regale my readers with what I deem the weirdest of all slug traits: reproduction. Being slow creatures, slugs tend not to encounter others of their own kind as much as they'd like. To account for this, they've developed an adaption strategy shared by many deep-sea fish who share the same problem: duo-gender individuals. Being "hermaphrodites" like this allows any two snails to mate, and makes it much easier for them to pass on genes. The "ninja" slug (Ibycus rachelae), which was first described in 2008 in Borneo, has adopted and even wilder reproductive strategy. Rather than allowing its mate to come to close quarters, it instead fires a harpoon-like "love dart" in order to pass on its sperm. Weird as that sounds, it's very effective.
My thanks for your attention, readers. I hope you found this interesting, if not entirely applicable elsewhere in life. I will be leaving again this week for the Odonata Society annual dragonfly hunt in Fall Creek and Ladysmith, Wisconsin, and so I should be posting  about my adventures there in a couple weeks.
Enjoy your summer, and as always, happy reading.