Thursday, September 6, 2012

Slimy Snails

Ever walked down a beach at the ocean and picked up sea shells?  These are the exoskeletons of a group of organisms known as Mollusks.  Mollusks are defined as soft-bodied invertebrate (no backbone) animals with a hard protective shell usually made of calcium carbonate (and slugs, which have no shell).  Most Mollusks live in oceans, but a few live in non-salty habitats, including ponds and damp environments like the forest floor.
Freshwater snails in our pond.
Snails are Mollusks with spiral shells, eyes on stalks that look like antennae, and a muscular foot for gliding along surfaces.  Here's a neat diagram of snail anatomy to get a sense of snails' body parts.  The pond at our outdoor classroom is teeming with snails!  If you sit and look into the pond for a minute, you'll start to notice black globs moving very, very slowly.  Pick one up - they don't bite - they really only eat plant material.  You now have a snail in your hand.  Say hello to your snail.  S/he will probably not be very happy to see you, which s/he will demonstrate by curling up into his/her shell.  S/he thinks you're going to eat him/her.
Snail recoiling into his/her shell for protection.
OK - this post is starting to get annoying!  What's with all the gender slashes?  Well, it turns out that most snails are both male and female, which is actually pretty neat. 

Snails breathe oxygen, just like we do.  Some use lungs and others use gills for breathing.  You'd think that land snails would use lungs and pond snails would use gills, but it's not that simple.  You'll find some of each kind both above and below the surface of the water.  You'll have to decide what you think about our snails' breathing method.  If they touch the surface every once in a while, they have lungs.  If they never come up, they are either dead or breathe using gills.  Since there are over 4000 species (types) of freshwater snails, and they are very difficult to tell apart, I cannot tell you what kinds we have.
Snail scaling the rocks behind our waterfall on a DIY trail of slime.
I know what you'd really like to ask is, "what's the deal with snail slime?"  Well, snails are gliders.  If you've ever tried to slide down a Slip 'N Slide without water, you know that you get stuck and it's no fun.  Well, snail slime works like water for a Slip 'N Slide, but much, much slower.  The snail constantly makes slime, slathers it across the surface of whatever it's gliding on, and makes itself a slippery trail.  Snails wave their muscles in their foot (the part of their body that contacts the ground) and push themselves along.  Whee!  If you place a snail on a piece of glass or clear plastic and watch from underneath, you can observe this phenomenon.  You may also see the snail's mouth as it drags along the glass trying to scrape up any bits of plant matter.  An interesting fact about snail slime is that you can buy a face cream made with it here.  I don't know why you would want to do such a thing, but if you really want to, it would be much cheaper just to let snails glide on your face.  In case you're not grossed out enough already, humans make a very similar substance in our bodies - mucus.  Mucus helps keep the insides of our mouths, lungs, stomachs and noses slippery so they don't get stuck together.
Blob of snail eggs on algae.
Snail populations work on a boom and bust cycle.  Where there is a lot of plant material available, such as decomposing leaves or algae, snails have enough food to produce a lot of offspring.  Our pond has lots of plant food available, so there are a lot of snails.  If you look carefully at a clump of algae from the pond, you may see a lump of clear gel balls - those are snail eggs.  When all the plant material is gone, the snails will mostly die off, but they will repopulate again when nutrients are available.  It's easy to keep snails in an aquarium, as long as you offer them some lettuce or algae from time to time.  Be careful though, if you leave too much lettuce in the tank, you will end up with hundreds of snails!
The most common type of snail in our pond.
Since our snails require fresh water to survive, and snails were not intentionally added to our pond, where do you think they came from?  There are two likely answers.  One is that snails or snail eggs were attached to the aquatic plants that were planted in our pond.  The other explanation is that snail eggs are sticky (from snail slime!), and they sometimes stick to birds' legs.  Any water birds that have visited our pond could bring or take snail eggs to or from our pond.
Another type of snail found in our pond, plus some neat clouds reflected in the water.

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