Ventus by Karl Schroeder description:
A novel of information apocalypse set in the far future. For a thousand years the sovereign Winds have maintained the delicate ecological balance of the terraformed planet Ventus. Now an alien force threatens to wrest control of the terraforming system away from the Winds…
not monsters. That one was just trying to protect itself."
"What was that silver stuff? It looked alive!"
"Dad told me about that one time. The mothers protect themselves with it. He said the stuff goes towards whatever's wettest. He said he saw somebody get covered with it once; he died, but the stuff was still on him, so they got it off by dropping the body in a horse trough."
Emmy shuddered. "That was an awful chance. Don't do anything like that again, hear?"
The excitement was over, and the rest of the crowd began to disperse. "Come, let's get you cleaned up," she said, towing him in the direction of the kitchens.
As they were rounding the reflecting pool, Jordan heard the sudden thunder of hooves, saw the dust fountaining up from them. They were headed straight for him.
"Look out!" He whirled, pushing Emmy out of the way. She shrieked and fell in the pool.
The sound vanished; the dust blinked out of existence.
There were no horses. The courtyard was