In message , Just Molly
writes
I do this on my nasturtiums. I put on a rubber glub, and run my
fingers alon any stems etc infested, then turn the leaves over so the
birds can see them. Almost as soon as I go indoors there are hungry
blue tits and finches eating mashed blackfly.

We have lots of blue tits and finches (I suppose because we're summer
feeding now), and more blackfly than ever this year, but I have never
once seen any kind of bird feasting on the blackfly ((
--
Klara, Gatwick basin