Incubation

The small reddish things are called 'galls'. These occur when an insect pierces the host plant and lays its eggs. The hose starts to build a structure which houses and feeds the insect's young until they are ready to hatch. ( https://en.wikipedia.org/wiki/Gall ).

When I first saw them, I thought they were walnuts but this is an oak tree. My housemate told me what they were.

[Yao RL]

Interesting to see what comes out.

[Mags]

Fascinating! They look like fruit on the branch.

[Joanne Diochon]

I too am wondering what will come out and will it be a single or a swarm.

[John Falconer]

Great shot.

[KV]

They look like a rather large berry or even an egg. Is that a stump on the left side?

[Faye Turner]

So interesting

[Shutterbug]

In the autumn they fall to the ground if you crack them open, you can see the holes where they were.

[Walks @ 7]

@yaorenliu @marlboromaam @gardencat @johnfalconer @kvphoto @fayefaye @shutterbug49 Thank you so much. I admit that this is first time that I've noticed these but I just might leave them be.

[Ann H. LeFevre]

They appear a lot- I'm never sure whether they are good for the tree or bad for it. Interesting shot.

[Walks @ 7]

@olivetreeann I am not sure about the long term benefit but nature really works in mysterious ways. I hope to go back in the near future and so what, if anything, has happened.