Ants, with more than 12,000 described species in the world (and the group on which I specialize as a naturalist), are among the better studied insects. Yet it's a good guess that the actual number is double or even triple that. In 2003 I completed a study of the "big-headed ants" of the Western Hemisphere, a genus (Pheidole) that has the largest number of known species and is among the most abundant of all the ants. At the end of my study, after 18 years of off-and-on effort, I had distinguished 624 species. A majority, 337, were new to science.
Only a dozen or so of the species have been closely studied. One of the smallest, I discovered, feeds on oribatid mites, which are usually much smaller than the letter o on this page and resemble a cross between a spider and a turtle. Oribatids are among the most abundant creatures of their size in the soil. A cubic foot might contain thousands of individuals. Yet I found that their diversity and habits remain largely unknown, much more than in the case of ants.
Life at the ground level is not just a random mix of species, not an interspersion of fungi, bacteria, worms, ants, and all the rest. The species of each group are strictly stratified by depth. In passing from just above the surface on down, the conditions of the microenvironment change gradually but dramatically. Inch by inch there are shifts in light and temperature, the size of the cavities, the chemistry of the air, soil, or water, the kind of food available, and the species of organisms. The combination of these properties, down to a microscopic level, defines the surface ecosystem. Each species is specialized to survive and reproduce best in its particular niche.
Soil studies, and especially the biology of the ground level, is growing rapidly into a major branch of science. Now bacteria and other microscopic forms of life can be identified quickly by the decoding of their DNA. The life cycles of increasing numbers of insects and other invertebrate animals, many entirely unknown to science, are being explored in the field and laboratory. Their physical and nutritional needs are coming clear, species by species. The Encyclopedia of Life, available in a single address (eol.org), is gathering all known information on each species and making it available free throughout the world.
A small world awaits exploration. As the floras and faunas of the surface are examined more closely, the interlocking mechanisms of life are emerging in ever greater and more surprising detail. In time we will come fully to appreciate the magnificent little ecosystems that have fallen under our stewardship.