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Now identified as Cicada orni by local entomologist. The best means of differentiating cicadas is by their song (http://www.cicadasong.eu/).
Beautifully camouflaged against the tree, I wouldn't have noticed this insect until it started chirping loudly just as I passed.
There seems to be no widely-agreed English common name for this species. The name I chose (Grey Cicada) produces a handful of Google results.
Good to know a local agrees with my ID. They sure are loud but are very easily missed visually. Only the males sing, by the way.
Nick Upton, naturalist and photographer.
They certainly are - I can hear them at the moment, chirping away outside. Thanks for the identification Nick!
Lat/Lng: 37.98, 23.75