Back in early spring, when just a few buds had cracked open, the world was constrained by a strip of pavement, a lawn, the driveway with the basketball hoop at the end, the dusty colors of sidewalk chalk. The Mission Mountains, Sapphires, Bitterroots - sheltering bears, mountain lions, and elk - were visible from various spots in the neighborhood; they and their inhabitants floated out of reach.

Because I spend so much time here on the porch, keeping an eye on my 3-year-old twins, checking that the boy doesn't run into the street, that the girl doesn't taste all the flowers, it was hard to miss the odd bees that swooped and dove one warm afternoon.

All kinds of wild bees come to glean pollen from the tiny patches of Montana wildflowers in our front yard, just a smattering of the 4,000 bee species native to North America. Many days, the air is thick with buzzing. Small ones with green stripes; big bumblebees that look clumsy until you watch their precise gestures; some striped like honeybees but more streamlined, as if they had been crossed with miniature military planes. A neighbor with a more ambitious prairie garden showed me the soil-dwelling bees living next to the peeling red paint of her steps. Large and black, daubed with yellow mid-back, these ones hummed just by my face as they headed to the porch swing.

Crawling underneath the swing, I looked up to see the tiny screw holes tamped with mud. One of the mud cells was empty, a hole punched in the middle, leaving hard dirt around the edges. Excavation with a pencil tip revealed bright yellow pollen packed at the back of the cavity. All the construction loosened the screws - one was almost out - and I fixed them before sitting back on the swing and wondering what was going on down there. All summer I checked back, but the holes remain sealed.

Now, fall has arrived with still no change. Weather reports suggest not just frost but snow. Prickly and brittle blanketflowers drop everything but the round seed heads at their center. Fringed sage, faint green to start with, loses even more color. We harvest our first pumpkin and put it on the front steps. The bees must be dead. The tightening of the screws and wrenching of the wood probably disturbed their wooden cells. Or maybe it was all the swaying. The kids are out, and I pick up a skewer to investigate.

As I break through the mud seal of one cell, a shower of dirt and bits of pollen rains down. A grey casing, swathed in rough threads, like some monk's rough-hewn garment, is tucked at the back of the hole. I rip one end open, expecting a pale, desiccated husk, but it's black inside. Then the black resolves itself into a thread-thin antenna that straightens as it pokes out. A leg, just at the edge of the tear, extends out, too.

I take it into the house to the kitchen table where it's warmer. At one point, antennae waving, two legs free now, the bee starts across the table, dragging the cocoon like a hermit crab. Talking to myself to calm my hasty hands - "don't crush it" - I use tweezers to pull it out. Like its parents, it is all black except the bronze film of wings, and tuft of gold behind the head. The face is black, too, with two gold arrows that point up like eyebrows of cartoon evil. It must overwinter in that perfect state and emerge in the spring to harvest pollen, mine mud, and look for a good cavity to lay in.

The kids thunder in and I sweep the cocoon and bee on a book and put it high out of harm's way. Hours later when I check back, the casing is alone, looking more empty than ever. The bee must have found its wings and zoomed off, into the wrong habitat, into the wrong season.

It leaves behind, in the broken bits and dust, a sense of wildness close at hand. More bees are in the porch swing, ready to be rocked through the cold. The surface of house, street, distant hills appears so calm and smooth, waiting for snow, but everything is, so subtly, shaking.

Kim Todd's most recent book, Chrysalis: Maria Sibylla Merian and the Secrets of Metamorphosis, will be out in paperback next month.