Can anyone identify these large... spider nests? Cotton balls?

Found these walking in Central Massachusetts. They look like big balls of cotton, about 4 inches across, they’re hollow with a big hole in the side, and they have twine securing them to the rock that looks awfully like store-bought string.

The others on my walk were convinced it was an art installation, I’m thinking some critter laid eggs in them. Thoughts?


That looks like a spider egg sac where the babies have hatched and grown big enough to leave. What kind of spider, I don’t know.


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