Fio,
I have also had these things. I probably still do because I have been fighting them for a couple of months and recently found some baby devils, no more adults though.
There are some good threads on wetwebmedia.com about them. In fact, I recently asked about them and Bob Fenner himself answered.
If you can get some of the colonies out easily, I have been doing FW dips and Coral dips (Lugols if you can find it). This seems to stun/kill them and then you can pick them off with tweezers and smush them.
From what I can gather, you have to QT them if you can and dip them about every week or so for a while ( a couple of months?) until you either don't see them anymore for a long period of time.
I also asked about a six line wrasse and was told by the Doctors site that they would eat the spiders. I bought one and put him in my QT. He is fat, fat, fat now and he doesn't get fed but once a day. I think he must be eating them because I haven't found anymore spiders.
I am by no means an expert and maybe someone else here can add or subtract to the above. Hope this helps some and good luck to us both!
