Monday, December 2, 2013

Pity the Slug



If ever there was a creature needing a better press agent, it is the slug.  From the mother who calls her late rising child a slug to the kids sprinkling salt on one to watch it shrivel up, slugs don't get a break.  They are the Rodney Dangerfields of the animal world.  There are slugs that live on land, in saltwater and freshwater, but lets stick to the land slugs.

On a recent field trip, we found this slug on the forest floor, minding its own business by crawling through the new leaf litter.  And just what is its business?  How about a major link in the food chain?

Dorsal view
Slugs and their armor covered cousins, the snails, inhabit the ground.  The name slug usually refers to an "apparently shell-less mollusc," a phrase referring to the fact that a few have internal or incomplete shells.  Those with a shell too small to retract into are called semi-slug, raising the question of why it bothers hauling around that apparently worthless shell.  It turns out that this is a way of storing calcium for future use.

Since the slug's body is mostly water, dehydration is a major problem (especially if a 6 year old is sprinkling salt on you in a precocious experiment of osmosis.)  This is the reason they prefer damp places like under rotting logs and leaf litter.  They also produce slime which helps to reduce evaporation.  One type of slime on their backs may make them harder for predators to grasp.  The slime they lay down as they travel is helpful to males seeking a mate as well as predatory snails looking for lunch.  Sex is a risky business - just ask a turkey gobbler responding to a hunter's call.

Even if it escapes predators and successfully mates, it may not be out of trouble.  In some species the male sexual organ can become irreversibly entangled with its mate. When that occurs it can only be separated by one of the partners in a process called apophallation .  Apo is Greek for "away from or separate, phallus is, well you know.  The details of the chewing process doesn't belong in this family blog but can be read about on Wikipedia under reproduction.

Underside (ventral surface) shamelessly exposed
Slugs are generally generalists, eating lots of veggies and other plants as well as lichen, fungi and even carrion.  Some are predatory, eating worms, snails and other slugs.  While gardeners are familiar with those feeding on flowers, herbs and vegetables, many are fungus specialists living under rotting logs and leaf litter. such as our friend above.

Now back to their role in the food chain.  Lots of things eat slugs, including birds, ground hogs, ground beetles, frogs, shrews, centipedes, moles, mice and even other slugs.  Red-bellied and brown snakes eat slugs and snails as a major part of their diet (coming soon to a blog near you on Snake Lips.)  And we haven't even touched on the other insects and parasites.

I would guess that you never have tried to identify a slug species.  Neither had I, but there are tools out there for that purpose.  One is iidtools.org which has information on slug anatomy and dissection, keying slugs and fact sheets on the various species.  It also has an interesting photo gallery although it loads very slowly.  (What did you expect, after all they are pictures of slugs!)

So slugs are important in the food cycle.  They may be the Rodney Dangerfields of the animal world, but hey, at least they get a lot of invitations to lunch .

1 comment:

  1. You have outdone yourself! I learned and laughed!

    ReplyDelete