"............and I have noticed a lot of red spider mites one
month ago in the garden. I have not seen a big quantity around the tree and
along the trunk (two or three), so I was not worried. But now, I am
.........."

I have my doubts about them being Red Spider.
If they are bright red, about half the size of a pin head and moving fairly
fast then they are red mites, and are in fact a predator of the red spider.
Red spider are a dull brick red and very hard to see with the naked eye,
they are mostly found by the presence of their web.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk
***2004 catalogue now available***