you may have the cocoons from the "Holly Blue butterfly"

which from its name the caterpillars eat the leaves of holly.

Gg

This might be yet another report of a mealy bug (unarmored scale insect) infestation. Can you send a photo of what you are describing?

Spiders have their eggs in silk cocoon like structures this time of year, but they tend to be a bit more spherical than caterpillar cocoons.

A photo would be very useful - it could be the egg masses of Cushion Scale, though this usually also causes sooty mould on the upper leaf surface.