Looks like one of the shield bugs.

the only place I could find pics of this were on a website in Russian - English translation of the name comes up as simply 'black and white shield bug'. It's not listed on the English sites at all, they have similar ones, but not this particular one, so I don't know what Latin name it has. Given I can't find it anywhere, its likely tis a foreign import, probably due to the hot summer, although maybe someone else has seen these before. Shield bugs tend to stick to the same few plants as food sources depending on species, but spend most of their time on the ground.

Back again - seems a bit more complicated than my previous answer - this might be what they call a mid instar nymph of the Southern Green Shield Bug - when fully mature, its much broader and just green.

Report the sighting online at http://www.brc.ac.uk/risc/southern_green.php