Posted: 25/05/2014 at 13:55
The tree is an elder. The insects are aphids.
Ladybirds and bluetits deal with the aphids in this garden, or you can use an organic spray or mix up a weak solution of Ecover washing up liquid and spray them with that.
However, I don't think they'll do much harm to your elder tree and they'll provide food for baby birds. I'd leave them alone.