Ooh, that's a bit confusing - you say you're from Shetland, but the flag displayed above is the USA one and it says USA...
A photograph would be very useful, and also knowing which variety of tree you speak of.

I would imagine it is a gall of some sort, but as said a photo would be best.

I would hazard a guess that its a town called Shetland in USA and that it is gall wasp ... could be oak.

I bow to your superior geographical knowledge, Mrbarret - mine's terrible, confirmed by the fact there were at least 5 countries I'd never heard of when the athletes were marching through the Olympic Arena!

She could actually be from the home of the Shetland ponies, though! We Yanks come from all over-my dad's family is from east Prussia (part of Poland, now), and my mom's is from Wales.

Not so different from what's laughingly known as 'English' then, Tugbrethil - we're almost all mongrels from all over...

I think that it's one of the strengths of our culture--though an occasional cause of confusion! : )

That's my view too...