Nymph On A Prickle

I was waiting for a phone call so didn't stray far from the house. I'd seen a hairy shieldbug on this thistle earlier in the day so went searching for it. No sign of it but I found this. I think it is a third instar nymph of a southern green shieldbug. I've never seen an adult, these insects arrived in the London area in 2003 on foodstuffs imported from Ethiopia.