"Jaques d'Alltrades" wrote
Blackfly. (Aphids)

Spray them with an insecticide such as Sybol (from garden centres,
hardware shops, etc), or with one of the water-down and put in sprayer
type.

They will sap some strength, but their main danger is spreading diseases.

There seems to be an absolute plague of the things here at the moment. I've
got them on several plants I haven't noticed them on in other years. Main
annoyance is that they've attacked the very first flower shoot of a yucca I
planted last year. Happily there are several ladybirds and their larvae now
getting down to business as well, so I'm hoping the aphids won't do too
much damage before it has a chance to flower properly.

So much for feeding the birds all winter - the bluetits don't seem to be
paying any attention.

--
Sue