Imagine picking up a live animal the size of a shoebox and eating it, bite after bite, without stopping until it's completely gone.

That's the way ladybugs eat aphids -- they just grab 'em and eat 'em.

I know this because I was staring at some curled, dying leaves on my dwarf apple tree in my dwarf backyard one summer day. Aphids were sucking the leaves dry, and I was wondering what to do -- until suddenly, a host of ladybugs flew in for a picnic. The aphids were soon under control, though enough survived to seed future generations and thus feed future generations of ladybugs.

The ladybugs had come from the yard of my next-door neighbor, an avid gardener, who had purchased a breeding stock of a local species some years before. Although her yard was as tiny as mine, she piled up leaves to serve as a ladybug habit in part of it. When aphids were out of season, she would place apple slices beneath the leaves to feed the ladybugs so they would remain in her yard.

That was my introduction to "backyard biodiversity," the art and science of providing appropriate habitat for native biota -- a practice that turns out to be critical for keeping the planet habitable.

Wildlife is increasingly threatened by development and farming, which destroys its habitat; roads, which dissect ecosystems; cars, which kill millions of animals every year; and invasive species, which can destroy entire ecosystems. Unless these trends are counteracted on both the macro scale, by limiting sprawl development and preserving natural areas, and the micro scale, by providing appropriate wildlife support within existing developed areas, species will continue to disappear, ultimately taking with them the ecosystems upon which human existence depends.

Fortunately, homeowners and even apartment dwellers can foster native biodiversity by providing the basic necessities -- water, food and shelter, aka habitat -- for our fellow species. Providing habitat is easy and inexpensive, and can actually save money on landscape maintenance, as natural habitats mostly maintain themselves.

The scale of the project can vary from a couple of flower pots on a balcony, containing plants that nurture local pollinators, to extensive waterways on a large property. A neglected corner of a typical urban yard will suffice to give a few plants and creatures a home, but allotting more space will allow you to build a more complex and interesting habitat.

Ideally, a home habitat will support a wide array of species and re-create the nutrient cycles found in natural ecosystems. Thus, organisms that break down organic waste, such as fungi and detritivores (e.g., worms and soil bacteria), would be as welcome as popular song birds and decorative native flowers. While predator and prey insect populations tend to balance each other out over time, circumstances might dictate that you manipulate the system in favor of certain beneficial species like ladybugs. Always keep in mind that native plants support native animals.

A good start for your habitat, then, might be some old lumber or logs set on the ground to rot, thus providing food and shelter for thousands of tiny organisms and their larger predators, as well as soil nutrients for plants. Brush and berries planted in the wood pile will provide shelter and food for a different array of species, while trees, if there's room for them, will shade and shelter the entire habitat.

Water must be clean -- birdbaths with stagnant water containing bird feces are poisonous -- and, ideally, free of chemicals such as chlorine that kill soil bacteria. Sunlight is the best disinfectant, so a fountain driven by a small solar-electric pump is a good design option. (Mosquitoes don't breed in moving water.)

Feed wild animals minimally and with caution. Dependence on an unbalanced diet provided by humans can weaken them, and excess food stock can attract pest species like raccoons and rodents. A well-designed habitat will generate enough nutrients to support abundant biodiversity.

There is a simple way to populate your home habitat: "build it, and they will come." However, you might need to introduce certain species or elements to create the balance you want at your ecological house, so be prepared to do some in-depth learning about your local ecosystem.