People seem to forget that if you use predators as a form of pest control
then you have to have a small amount of the pest permanently resident.
With the move away from chemicals and with more nurseries going over to
predators then the chances of having one or two pests on a bought in plant
are much greater.
Secondly think of the "Invasions" of spiders over the English Channel at
times.......the young spiders climb up plants/trees etc then let out thread
till it is caught by the wind which carries them off to a new area,
sometimes 40 or 50 miles away, No reason why Red spider cant do the same.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk