Green leaf wasp

Tenthredo mesemola is a big species, composed of two colours only: black and green. The upper side is black, except for some spots near head and neck and the shield. Even the upper side of the legs are black. On the front legs this often is less apparent, as the line of black is very thin indeed. The underside of the animal is green entirely. The larvae are found on various plants, Salix species in particular. The adults are often seen eating nectar and pollen on white flowers. But the adults also hunt for small flies which they suck on. This is remarkable for a Sawfly species, for almost all are strict vegetarians.
(text from http://www.gardensafari.net/en_picpages/tenthredo_mesomela.htm)