Not horse related - Very odd acorns!! What are these?

[dollymix]

Any idea what these are growing on the scorn trees near us? Don't think I've ever noticed then before? Some look like they are bits of green popcorn erupting from the acorn cup?

 

[Sussexbythesea]

Caused by a wasp laying eggs.

http://www.naturespot.org.uk/species/knopper-oak-gall-wasp

 

[ameeyal]

Well I never. !!!

 

[dollymix]

Thanks! Was driving my dad mad!!!

 

[Sugarplum Furry]

Gall wasp eggs. Or rather, that's what's inside them. I found some on an oak tree last week and was intrigued, had to do a Google search. Gall wasps started invading the UK from the continent in 1962 so not a native species. There's the oak tree gall wasp, the galls turn into those weird brown 'shells' that you see on oak trees, and the dog rose gall wasp which produces bedeguars, more commonly known as robin's pincushions.