"Jesus," Bobby said, staring through the binoculars.

"What? What is it?"

"It's a body being dragged," he said. And then, in a funny voice, he said, "It's Rosie."

Gunning the bike, I took off with Mae, running along the edge of the ridge until it sloped down toward the streambed floor. Bobby stayed where he was, watching Rosie's body. In a few minutes I had crossed the streambed to the other bank, and was moving back toward his light on the hill.

Mae said, "Let's slow down, Jack."

So I slowed down, leaning forward over my handlebars, trying to see the ground far ahead. Suddenly the radiation counter began to chatter again.

"Good sign," I said.

We moved ahead. Now we were directly across from Bobby on the ridge above. His headlamp cast a faint light on the ground all around us, sort of like moonlight. I waved for him to come down. He turned his vehicle and headed west. Without his light, the ground was suddenly darker, more mysterious.

And then we saw Rosie Castro.

Rosie lay on her back, her head tilted so she appeared to be looking backward, directly at me, her eyes wide, her arm outstretched toward me, her pale hand open. There was an expression of pleading-or terror-on her face. Rigor mortis had set in, and her body jerked stiffly as it moved over low shrubs and desert cactus.

She was being dragged away-but no animal was dragging her.

"I think you should turn your light off," Mae said.

"But I don't see what's doing it… there's like a shadow underneath her…"

"That's not a shadow," Mae said. "It's them."

"They're dragging her?"

She nodded. "Turn your light off."

I flicked off the headlamp. We stood in darkness. I said, "I thought swarms couldn't maintain power more than three hours."

"That's what Ricky said."

"He's lying again?"

"Or they've overcome that limitation in the wild."

The implications were unsettling. If the swarms could now sustain power through the night, then they might be active when we reached their hiding place. I was counting on finding them collapsed, the particles spread on the ground. I intended to kill them in their sleep, so to speak. Now it seemed they weren't sleeping.

We stood there in the cool dark air, thinking things over. Finally Mae said, "Aren't these swarms modeled on insect behavior?"

"Not really," I said. "The programming model was predator-prey. But because the swarm is a population of interacting particles, to some degree it will behave like any population of interacting particles, such as insects. Why?"

"Insects can execute plans that take longer than the lifespan of a single generation. They can build nests that require many generations. Isn't that true?"

"I think so…"

"So maybe one swarm carried the body for a while, and then another took over. Maybe there have been three or four swarms so far. That way none of them has to go three hours at night." I didn't like the implications of that idea any better. "That would mean the swarms are working together," I said. "It would mean they're coordinated."

"They clearly are, by now."

"Except that's not possible," I said to her. "Because they don't have the signaling capability."

"It wasn't possible a few generations ago," Mae said. "Now it is. Remember the V formation that came toward you? They were coordinated."

That was true. I just hadn't realized it at the time. Standing there in the desert night, I wondered what else I hadn't realized. I squinted into the darkness, trying to see ahead. "Where are they taking her?" I said.

Mae unzipped my backpack, and pulled out a set of night goggles. "Try these." I was about to help her get hers, but she'd deftly taken her pack off, opened it, and pulled out her own goggles. Her movements were quick, sure.

I slipped on the headset, adjusted the strap, and flipped the lenses down over my eyes. These were the new Gen 4 goggles that showed images in muted color. Almost immediately, I saw Rosie in the desert. Her body was disappearing behind the scrub as she moved farther and farther away.

"Okay, so where are they taking her?" I said again. Even as I spoke, I raised the goggles higher, and at once I saw where they were taking her.

From a distance it looked like a natural formation-a mound of dark earth about fifteen feet wide and six feet high. Erosion had carved deep, vertical clefts so that the mound looked a little like a huge gear turned on edge. It would be easy to overlook this formation as natural. But it wasn't natural. And erosion hadn't produced its sculpted look. On the contrary, I was seeing an artificial construction, similar to the nests made by African termites and other social insects.

Wearing the second pair of goggles, Mae looked for a while in silence, then said, "Are you going to tell me that is the product of self-organized behavior? That the behavior to make it just emerged all by itself?"

"Actually, yes," I said. "That's exactly what happened."

"Hard to believe."

"I know."

Mae was a good biologist, but she was a primate biologist. She was accustomed to studying small populations of highly intelligent animals that had dominance hierarchies and group leaders. She understood complex behavior to be the result of complex intelligence. And she had trouble grasping the sheer power of self-organized behavior within a very large population of dumb animals.

In any case, this was a deep human prejudice. Human beings expected to find a central command in any organization. States had governments. Corporations had CEOs. Schools had principals. Armies had generals. Human beings tended to believe that without central command, chaos would overwhelm the organization and nothing significant could be accomplished. From this standpoint, it was difficult to believe that extremely stupid creatures with brains smaller than pinheads were capable of construction projects more complicated than any human project. But in fact, they were.

African termites were a classic example. These insects made earthen castlelike mounds a hundred feet in diameter and thrusting spires twenty feet into the air. To appreciate their accomplishment, you had to imagine that if termites were the size of people, these mounds would be skyscrapers one mile high and five miles in diameter. And like a skyscraper, the termite mound had an intricate internal architecture to provide fresh air, remove excess CO2 and heat, and so on. Inside the structure were gardens to grow food, residences for royalty, and living space for as many as two million termites. No two mounds were exactly the same; each was individually constructed to suit the requirements and advantages of a particular site. All this was accomplished with no architect, no foreman, no central authority. Nor was a blueprint for construction encoded in the termite genes. Instead these huge creations were the result of relatively simple rules that the individual termites followed in relation to one another. (Rules like, "If you smell that another termite has been here, put a dirt pellet on this spot.") Yet the outcome was arguably more complex than any human creation. Now we were seeing a new construction made by a new creature, and it was again difficult to conceive how it might have been made. How could a swarm make a mound, anyway? But I was beginning to realize that out here in the desert, asking how something happened was a fool's errand. The swarms were changing fast, almost minute to minute. The natural human impulse to figure it out was a waste of time. By the time you figured it out, things would have changed.

Bobby rumbled up in his ATV, and cut his light. We all stood there under the stars. Bobby said, "What do we do now?"

"Follow Rosie," I said.