Excellent, thanks. Where can I find out more about these intriguing wasps? And am I right referring to them as spider-eaters?

The adult wasps don't eat spiders themselves (though they probably imbib the preys hemolymph) but provision their nests with spiders/immature spiders for their larvae. For many solitary wasps, the best bet is to start with: Naturalists Handbook 3: Solitary Wasps by Yeo and Corbet (2nd edition paperback). Also, if you haven't already, joining BWARS will get you a members handbook with lots of general info and literature suggestions etc.