What are these on our town’s oak tree?

[BarnOwlFlying]

Oak tree seems healthy enough but I’m curious to improve my knowledge.

Does anyone know what these things are on the leaves? There are round Cheerio type discs and round, flat, plate like discs.

There is also something weird on quite a few of the acorns: you can still see the acorns to start with, then they seem to get encased in a hard brown thing.

Sounds like gall wasps

https://www.rhs.org.uk/biodiversity/oak-gall-wasps

Very similar to your pic:

https://www.heenecemetery.org.uk/species/spangle-gall-wasp

Very interesting. Thank you.

That's 4 different species of gall wasp. First picture left is an artichoke gall. The one attached to the acorn itself is a knopper gall. The Cheerios disc with a hole on leaves is a silk button spangle gall. The flat disc is a common spangle gall.

I'll admit I had to look up the names for 3 of the 4 😁 The insect species themselves look pretty boring to me, but their different galls are quite cool.

It's a very healthy oak supporting that many species! You'll only find these on oaks, not on other species. You could probably find the marble gall on it too - the classic round one people usually think of when they think of galls. I think you can ground that one up with iron and make a purple ink.

https://www.suffolkwildlifetrust.org/news/hunting-galls there's a spotter sheet at the bottom of the page