We fished this guy out of the pool. He sat for a while drying out before flying away. Just long enough to get a couple of [admittedly dodgy] photos of him. I couldn’t identify him from our insect book, so I posted his pic on the Natural History Museum’s ‘bug forum’.
Thanks to ‘jaguardondi’, a retired entomologist, who identified it as a scoliid wasp, recognisable by its four 4 yellow abdominal spots. Here’s the link for the NHM http://www.nhm.ac.uk/natureplus/thread/11281
And here are two other, better pics, of a scoliid wasp.

5 to remember
una avispa – a wasp
un rato – a while
bastante – enough
jubilado/a – retired
el/la entomólogo/a – entomologist

‘Insects, Spiders and other Terrestrial Arthropods’ from Dorling Kindersley