When I first moved into my house, the second thing I wanted to do was put in a pond. I bought a litlte 50 gallon plastic pond from Lowe's and let the rain fill it. I kept minnows in it, had a UV filter, and before long it filled up with snails too. Before long though, it became more trouble than it was worth and the family decided it had to go.
I decided to try to keep a little bit of my pond alive in a few old pickle jars. Using aquatic plants from the pet store and water from my pond, I made about six different jars full of various bits of life. I sealed them up and set them in windowsill; two years later - two of them are still going strong. The picture above are the two sealed ecosystems in question - full of plants and snails and tiny little bugs.
It's amazing what sort of life is hiding in simple rainwater. With this cheap little project, you can start something that's far more interesting than any houseplant, and requires no more maintenance than turning a jar a little once a month or so.
Step 1: Gather Your Materials
1) First, you'll want to get a big pickle jar with a good lid. Metal is best, but use what you can get.
2) You'll want to go by the pet store and get some cheap little aquatic plant. Something with a lot of leaves is best. I usually put a small piece of lucky bamboo in there as well (It's usually cheap, and a little luck never hurt.)
3) You'll need about a cup of topsoil and some gravel or pebbles for looks. Use anything you find aesthetically pleasing.
4) Optional: Extra Snails. Ask the pet store if they have any nuisance snails. Usually these are tiny little snails that grow in tanks and are usually unwanted. If you ask for them, they'll often give them to you for free or nothing. Later on you will go hunt for your OWN snails, but having multiple species of snails gives you a better chance at finding the right balance that will make an ecosystem that lives. You see the bag of little black cone-snails I got. Mind you, you do NOT want zebra snails or Mystery Snails. These guys are WAY too big and will eat far too much.
Step 2: Arrange.
Get in touch with your inner feng shui here and arrange your plants in your jar. Sprinkle your dirt over everything, and then sprinkle the gravel/pebbles over everything. Don't worry too much about getting everything perfect, because when you add water, everything will go all pear-shaped on you. Still though, getting things arranged nice now will save you some effort later on.
Step 3: Take a Hike!
Get your boots on because you are going to need to head outside for this next step. You'll want to go find some natural water in your area. Lakes are great, but even something like a rain runoff area often houses a rich plethora of life. I took a trip down to the flood plains near my house and found the tiny little foot-wide seasonal creek.
You'll find your next three vital ingredients here. Bring a small cup or something to scoop with.
Also - LOOK OUT FOR SNAKES! They love places like this. Depending on where you live, Snapping turtles might be a concern as well. I saw one in this very creek a few years ago bigger than a hubcap. I'm pretty sure neighborhood kids tell stories about that monster.
Step 4: Moss.
This simple little aquatic algae is one of the biggest powerhouses in your jar. While your big plants might not make it, but THIS stuff will grow to use any carbon dioxide that your other living bits give off. It will also fill up with bubbles rather quickly. Make sure to get at least a pinch of this stuff. You only need a little bit, it grows quick.
According to user SpikyIke this particular example looks like Oedogonium. When picking algae, make sure you go for solid green, NOT anything blue/green.
Step 5: Avoid This.
If you are going to a creek, avoid the polluted areas. Rain run-off carries all the grime out of every yard and off of every parking lot for miles. If you go further down the creek, you'll find that grass and rocks tends to filter some of this out. If you are going to a lake, avoid inlets. You want to find a place where the water isn't really quick-flowing, but you don't want stagnant.
Step 6: Snails!
These little guys are what you are really here for! Find a handful of these little snails. Try to get at least ten or fifteen of them of varying sizes. I happened to notice that my tiny creep is simply swarming with ditch minnows. You normally will NOT want anything as active as a fish. The poor little guys will likely starve to death. Fish are far too metabolically active to survive a slow and delicate environment like the one you are putting together.
Step 7: Water.
Now this is the vital step. You'll need to get this natural water for your jar. You will NOT want tap water. Tap water is generally sterile and doesn't come with all the little bits and bobs you need for an environment to really come together. When this really sets up, you'll have a chance to have just about anything in there. I've seen everything from water fleas, to mites, to a full mosquito larvae hatch into an adult while sealed in!
When you pour the water in, be careful, but understand that it WILL turn into a muddy mess for a while. This is normal.
Step 8: Add Everything Else and Wait.
Add all the other stuff you have, in this case, my store-bought snails.
Rearrange your plants as best as you can, and wait. It's a foggy dirty mess right now, but time will fix that.
Step 9: The Fog Clears
After a full day of letting things settle, you'll start to get an idea of what your little world will look like. I added some more gravel sprinkled over the open space in the center for effect, but that kicked up more silt.
Just seal the jar up tight and leave it in a windowsill that gets indirect sun. You don't want DIRECT sunlight, because it will heat your little world up too much, and your algae will grow out of control. Every month or so, rotate it about 90 degrees.
Don't be too disappointed if some of your little world don't make it. It takes a very delicate balance to make things work just right. If they go a few months if everything turns brown, you'll know it's dead. If things DO go all brown, FOR THE LOVE OF ALL THAT IS HOLY don't let the jar come open! It will stink like a thousand hells.