What's this?

[TeresaW]

I found these on oak leaves today, fairly young tree, and these were on falling and attached leaves all over. Are these insect of fungi?

[Elean0r]

They look like Common Spangle Galls,

[Deer Stalker]

Hi Teresa.

They are Spangle Galls made by the Gall Wasp Neuroterus quercusbaccarum.

[TeresaW]

So that's what they are! Thank you.

[ChrisR]

I always rather like Oak galls ... especially spangle galls ... they have such amazing shapes If you are looking at an Oak tree in Spring when they are in flower look around the leaves on the lower branches for little black wasps sitting under leaves - these will probably be the Neuroterus wasps ovipositing and it's their larvae that create the gall to live in and provide them with food

[TeresaW]

I was fascinated by the detail on them, and twice as pleased with the photos if I say so myself

Do they harm the tree at all?

[thunder]

Originally Posted by TeresaW

I was fascinated by the detail on them, and twice as pleased with the photos if I say so myself

Do they harm the tree at all?

No, not in any serious way.

Watch under the trees once the leaves start to fall, you may well see flocks of tits and other birds pecking at the galls, feeding on the larvae inside.

henrya

[ChrisR]

Originally Posted by TeresaW

Do they harm the tree at all?

Well, they are parasites so slightly ... but the damage would be hardly noticeable really. The egg is laid in the leaf tissues and when the larva hatches it secretes hormones that forces the tree to grow the gall ... the larva continues to secrete hormones from inside the gall throughout its life. The gall serves 2 main purposes - as a safe home for the vulnerable larva (to protect it from parasitoids and from dehydration) and (ironically) as a food source because the tissues inside the gall are actually more nutritious to the larva than if it had just eaten the leaf.