S'ok. Just looked at the link that Dovefromabove gave. They apparently can harm gardens that have fruit bushes as they eat the sap and weaken the plant. Only fruit I have is strawberries and an apple tree that has never produced any fruit in the three years I've had it so I'm not going to do anything. Thaks for the link, Dove.
I have quite a few on one particular lavendar plant (maybe 6 or 8) it is the plant in most shade - would that encourage them?
Sarah, squash them or just leave them. They don't do any good though.
If they aren't actually going to destroy everything, I'll just leave them. Between the aphids/slugs/blackspot/ants/rubble and next door neighbour and his cctv camera I can probably get by without slaughtering them as well ....
That's interesting Sean, the rhs site says that the eggs have overwintered so I must have bought the lavendar with them already attached. Hooray, not a garden infestation for once.