Baby Sputniks?

Also looking like something from a far-off galaxy are these white structures, found under an oak leaf at WWT Penclacwydd some weeks ago. I noticed them when I was leaf-mining and I`m sure that they are nothing to do with moths, but has anyone any idea or suggestion as to what they are please?
I`ve seen them only once since, on another species of tree (but which tree and where, I cannot remember). They cannot be frequent, as I`ve been looking at a lot of leaves during my leaf-mining activities!
Postscript: Thanks to Sam putting me on the right track, I now believe that they are the eggs of the spider Paidiscura pallens.