Remember those caterpillars I found on my client’s pelargoniums?
Well – thank you to all who replied. Plant Mad Nige offered a tentative ID as an Angle Shades Moth – but here’s the pic of their caterpillars from the RHS’s advice sheet on the subject:
(image: Tim Sandall).
Not really very similar to my little critter:
But enter the RHS’s Principal Entomologist (no less), A J Halstead, who suggests my little friend is a rather more humbly-named Cabbage Moth – aka Mamestra brassicae. I looked this up on UK Moths – and sure enough:
(picture (c) Dave Griffin)
I think we have our culprit. Sadly he is a culprit, too – the moth is described as a “notorious pest” on UK Moth’s info page on the subject, scoffing not only all members of the brassica family but clearly pelargoniums too.
Still – I love solving a good mystery. Now I have to go murder a lot of rather pretty caterpillars…
Sally Nex 
Well, you can’t find a better authority than Andrew. He’s the absolute beez kneez when it comes to bug i/dsGlad you got the problem identified. Now all you have to do is solve it. Are there few enough caterpillars – and are you tough enough – to pick and squish?
thanks for volunteering your guess anyway nige – I thought you came pretty close :DI’m dreading having to squish the things… they’re quite big… I think I might go for the pot of salty water option. Or just ship them somewhere a long way away where they can’t do any more harm (at least, not to people’s gardens, anyway)