'Into the apparitions of the sky'

"I saw the spiders marching through the air,
Swimming from tree to tree that mildewed day
In latter August when the hay
Came creaking to the barn. But where
The wind is westerly,
Where gnarled November makes the spiders fly
Into the apparitions of the sky,
They purpose nothing but their ease and die''

-- From"Mr. Edwards and the Spider,'' by Robert Lowell