Butterflies In Decline - But Why?

This was a pretty good summer for breeding hosts of butterflies but - where were they? Numbers are reportedly heavily down. Our handsome buddleias should have been teeming with the little beauties - but they weren't.
The only good news was that we saw a greater variety of butterflies in the city than we have ever seen before.
In a typical season, we would see six or seven species but this last summer, we were comfortably into double figures including: two sizes of tortoiseshell, large and small whites, ringlets, skippers, peacocks, speckled wood, small blue, red admirals, possible powdered yellow, possible painted lady or two, commas, meadow browns and the odd fritillary.