Alasdair

I wouldn't have thought they were aphids if they are jumping. This looks more like a larval bug which is maturing on your elm. I am prety sure i have seen these bugs before in a magazine i collected as a youngster, i'm feeling really familiar here. I'll have a look tonight and see what i can find.

The last picture looks kinda like a cicada or something (just by the head). My best guess is some form of leaf-hopper.

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I can feel another "I wish that was my tree" moment coming on...
Currently studying BSc Plant Biology at the Universty of Wales, Aberystwyth