Not aliens…

… but the galls of the oak knopper wasp that are falling in my garden from next door’s oak tree. They’re rock hard, sticky and numerous.

From the Woodland Trust website:
“ The knopper gall is a relatively new arrival in the UK as the wasp only arrived in the 1950s. It’s found mostly on pendunculate oaks in England and Wales. The wasp, Andricus quercuscalicis, lays its eggs on the freshly pollinated flowers of the oak, causing the offspring to deform the acorn for its own uses. This gall develops over the summer and falls to the ground in autumn when the larvae emerge.”
https://www.woodlandtrust.org.uk/blog/2018/07/galls-to-spot-this-year/

The extras show just how weird the shapes are, twisting the acorn out of almost all recognition.