Putting the rain to work

Category: Water sources
Required points: 1
Suggested sources: Birdbath, Lake, Stream, Seasonal Pool, Ocean, Water Garden/Pond, River, Butterfly Puddling Area, Rain Garden, Spring

My little lot is not blessed with a pond, a stream, a spring, or beachfront, so it's necessary to add a built element to meet NWF's water requirement. I've no interest in attracting mosquitos, so birdbaths and similar standing-water features are off the table. A water-feature that wouldn't attract mosquitos required a little thought.
A few years ago I was on a backpacking trip as part of a literature class (think Thoreau, Emerson, Ed Abbey, Gretel Ehrlich, Linda Hogan, Annie Dillard, &c), when I had the most remarkable encounter with butterflies. Eight of us, or so, were hiking part of the C&O Canal Towpath near Harpers Ferry. It was the first week of July. It was hot. It was humid.
We stopped on a sandy, shaded bank of the Potomac to have lunch. Just beyond the shade, where the lean river had receded to expose a large patch of mud, hundreds of little white butterflies were mulling around on the ground. After a moment, they noticed us and swarmed us. They landed all over our clothing, unfurling their curly butterfly tongues.
The butterflies were cabbage whites, and the reason for their interest in us was salt- more or less the same reason they had been mining the river bank. As it happens, butterflies need to ingest minerals and salts that they can't get out of plants. Instead, they seek it out in exposed mud, bird guano, and even dried sweat.
We can give butterflies a hand by creating a feature that offers them the salts or minerals they need. One of the simplest ways to do this is to create a butterfly puddle by burying a bucket or other impervious container in the ground, up to its rim, and filling it with soil. When it rains, the soil in the container becomes saturated quickly, and the impervious walls keep the water in place. Since the container is ultimately full of mud, rather than standing water, mosquitos can't lay their eggs in it. Any overflow recedes into the surrounding soil fairly quickly.
In keeping with the goal of a self-maintaining system, I buried a rectangular 2-gallon plastic tub at the place where my downspout empties into my yard. I added little pea-gravel to the hole I surgically dug, so that it'll be easier to move the tub if adjustments are necessary. Most of the soil went directly back into the plastic container (where it will provide the minerals the butterflies are after), while the small amount of excess soil (and a few annelid worms) have found a new home in my composter. Now, every time it rains even a little, the puddle is recharged, and the impervious tub keeps the little patch muddy for a few days.
The plastic tub was an extraneous denizen of my basement, so I'll call its cost $1, since that's about what I'd expect to pay for such a thing at a yard sale. To buy a new one would be a few dollars more, though a variety of disposible plastic containers (read "free") or containers made from more benign materials would do the trick.
Again, if the rain ever stops when I'm at home, I'll update this with a picture from my own yard. For now, enjoy these puddling swallowtails, courtesy of Western Kentucky University.