'Whortleberries' sound to me like something Rambling Syd Rumpo would have encountered whilst nurdling his splod!
(There's a more accurate definition here:
http://www.everythingexmoor.org.uk/encyclopedia_detail.php?ENCid=1078 )
However I'm reminded that, about half a century ago, my father and I spent several hours collecting blackberries on Rushmere Heath (on the edge of Ipswich), so that my mother could make 'bramble jelly'. What we didn't know was that they must recently have been attacked by some sort of fly so that, by the time we got them all home, they were covered in thousands of maggots!
Uugh!