The weasel scampered through a narrow sluice carved in the snow by water dripping off our roof. Only its rapid movement caught my eye, its white winter fur making it nearly invisible against the white ground. In its mouth it carried a fat brown vole.

Last summer, weasels were boldly about, wearing their tan summer coats, and eyeing the chickens that free-range our peach orchard. This was a worry to us. A single weasel can ravage a flock, leaving many birds dead, their necks bitten, as a storehouse for future meals. Our chickens suffered no attacks, but by midwinter two neighbors had lost many to weasels. So after my sighting a long discussion ensued.

A weasel (or ermine, as the short-tailed weasel is sometimes called, especially with its white winter coloration) can fit its slender body through a mouse-sized hole so we could only hope that our chicken house was secure. Maybe we should trap it, we thought, just to be sure. But it had killed a vole, the worst pest on our farm. In some winters, voles have badly damaged greenhouses full of winter greens, and, outside, tunneled up perennial beds and girdled young trees. A weasel, we’d read, will eat a vole a day. Perhaps the elegance of this small white creature swayed our minds as well, and we let it stay. So far so good.

A farmer must play hunches and make compromises between the good that wild creatures do and the occasional risk you take to enjoy an environment rich in them. At such times of decision it’s worth noting how inexperienced humans are at farming when compared with those who have done it for millions of years. Species as diverse as marsh snails, leaf-cutter ants, termites and bark beetles maintain gardens where they cultivate fungi for food, fertilizing them, grooming them and protecting them from disease.

The most remarkable agronomists are the various species of farming ants. Some have developed their own strains of domesticated aphids, which they manage like cows or sheep. The food crop is a sticky sap called honeydew — plant sap that has passed through the aphids’ digestive tract. To stimulate this secretion, the ants milk the aphids with their forelegs and antennae. They keep their beasts docile and fenced by spreading a tranquilizing chemical with their feet, herding the aphids to food plants as needed. Ants’ mouth glands can apply a chemical to suppress aphid wing development, and if wings do appear they are bitten off. Ants attack aphid-eating predators such as lacewings and ladybugs. Unlike us, they do all these things without hesitation or doubt.

With a process so ancient and so mutualistic, it is hard to say who is calling the shots and who is enlisting whom. It makes you wonder: Did that weasel make a deal with us? He spares our chickens, we spare him and, except for the voles, everybody wins.

Damrosch is a freelance writer and the author of “The Garden Primer.”

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