The Sexual Life of Slugs: Molluscs II

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Animal Phyla

Introduction

A 1600 Work I

Bill Long 5/12/07

The Terrestrial Slugs--In Your Garden and Elsewhere--But Mostly on the Sexual Life of the Slug

As you see, by checking out the categories on the left, this "page" is devoted to a series of essays on the various animal phyla. I have decided to take a few examples of each phylum in order to understand and share a small slice of nature with you. I decided to study slugs for my Mollusca category because one of the words in the 2003 National Spelling Bee was limacine, and I hadn't previously seen the word. It means either pertaining to the Limacidae--a family of land-snails (slugs)--or viscous or slimy, like a slug. The Latin behind it is limax. This essay tells you about the slugs living on land, which are not so beautiful as their sea-slug cousins (some pictures of those Nudibranchia are here). I am not particularly interested in telling you how you can control an infestation of slugs in your garden or get rid of them with beer or salt (the latter is, according to several internet writers, a cruel way of killing the slug); the Oregon State or Washington State University Extension web pages will give you that information. By the way, I don't think we have a word in English to denote killing slugs. There ought to be such a word. After all, we have herbicide, fungicide, rodenticide, to name a few. There is a word molluscicide, which would refer to "offing" any mollusk; I suppose we have to content ourselves with this one, though I would like to lobby for limacide.

Just to let you know, I am most interested in discussing the sex lives of slugs in the remainder of this essay but first, a word on classification. We have seen that all slugs are Gastropods (Class), while the terrestrial slugs are of the Order (or superorder) Pulmonata. The suborders of Pulmonata are defined primarily by the number of tentacles and the number of eyes on the head. For example, the Basommatophora have one pair of tentacles with an eye at the base of each, while the largest Order/suborder, the Stylommatophora, has two pairs of tentacles with the eyes at the tip of the upper pair. These tips can be retracted inside the tentacles. The two pairs of tentacles pick up on light (the large upper pair) and smells (the lower pair). A land slug also is covered in much of its body by a mantle, under which are the anus and lungs, while a pneumostome, a "breathing hole" is on the right side of the mantle. It moves, however slowly, by one "foot."

Mating/Reproduction

One of the most fascinating parts of a slug's life, at least from the perspective of we humans in another phylum, is their mating process. This web site has some fantastic photographs of the mating of a pair of Leopard Slugs (Limax maximus, family Limacidae). You should know at the outset that these slugs are hermaphroditic--possessing both male and female characteristics (I think they are "male" first and then develop "female" organs). Here is a brief description of what I see. First, there is a long mucus cord, about a yard in length, from which the two slugs are suspended. Then, when they are sure that the slime will "hold," they begin the mating process. Part of a sexual organ becomes "everted," which means that it extends out from the body. It is a wonderful translucent white, with the deepest tinge of blue. First the lower slug everts. Then the top slug everts its sexual organ and they become entwined in a rich and closely connected field of hollow blue. This exchange and entwinement results in each of the pair becoming inseminated. Utterly fascinating and beautiful, don't you think?

Sex and the Banana Slug

The banana slug, Ariolimax columbianus (family Arionidae) is not only famous for being the mascot of the University of California, Santa Cruz, but because it runs into a potential problem in sexual contact. This fascinating web site of a Ph. D. student who is studying the mating habits of banana slugs answers lots of questions as well as provides a video of what can happen when these guys/girls mate. His study was on sexual conflict in hermaphroditic mating partners. It sounds like it should be the headline in the National Enquirer, but it is in fact the focus of a sober dissertation. Here is the web site. In any case, the first several photos of his site show some kind of "foreplay," where the slugs line up in a "yin-yang" type of position, with heads touching, since the genital opening is near the head. The slugs then engage in some biting of the genital areas of the other. Then, the penis, which is about an inch or two in length, will be inserted into the other. Now I will quote from the "expert:

"When they mate, they insert their penises into each other at the same time. The unusual thing (in case you don't find that unusual enough!) is that sometimes, but not always, when they finish mating one slug will chew the penis completely off the other, a process called Apophallation. Sometimes it happens that both slugs engage in chewing so that at the end of the mating encounter, both slugs are penis-less."

He is even kind enough to provide us with a compressed-time video of one of the slugs chomping off the other's penis. Here it is, for those that aren't faint in heart. Finally, he gives us a longer video (it took about two hours for this act to happen) which shows a slug biting off its own penis because he cannot lose his erection. Here is that video, which takes quite a long time to load. They ought to invent some kind of reverse-Viagra to help this guy out. But in fact he is out of luck. Our Ph.D student has coined a new word for the phenomenon of biting off your own penis--autoapophillation. Wow. I wish the dictionary-makers would be more progressive and give us all the words from the sciences; I could really hit this one out of the park.

Conclusion

I spent so much time on the mating habits of slugs, even though everyone else seems to want to describe which plants they eat and how you can get rid of them, because I want to inject, no pun intended, a new feature into the common understanding of slugs. When we accuse a person of being "sluglike" or "sluggish" or a "slug" today, everyone thinks that we mean the person is slow-moving or lazy. Well, with what we know about the sexual habits of slugs now, I think we can use the word "slug" now to mean someone who: (1) gets "entangled" deeply in gender relationships; (2) produces a wonderful and unique "product" when uniting in sexual contact; (3) or has a habit of biting off or getting his penis bitten off in encounters.... Can't you see the way that the word limacine, which really got me started on slugs, has lots of possibilities to it? Only problem is, that if this new context for limacine develops, they definitely coudn't use it in the Kids Spelling Bee. Can you imagine the pronouncer trying to tell the kids what my word limacine means? Even the adult spelling bee wouln't touch it with a ten foot strand of mucus.

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