Bedstraw Hawk Moth
The caterpillars that I have found have been on a willow herb Epilobium adenocaulon or on a bedstraw known as Cleavers or Goosegrass Galium aparine, though I once had one brought to me on a potted Fuchsia which had been decorating the stage during a high-school graduation ceremony. The specific name is sometimes seen as galii, which in principle is more correct than gallii, but presumably the misspelling gallii pre-dates galii and must, by the rules of taxonomy, stick. The young caterpillar is green with longitudinal stripes and is unremarkable. The full grown caterpillar has several colour forms, of which a selection is shown, any of which can fairly be described as spectacular.