do any of your plants have lots of webs around them. Tortrix moth rings a bell but it seems late in the year but it has been mild. Don't know if you get this one in spain though.

Hi Seaburngirl - no, there don't seem to be any webs round my plants - my neighbour has pine trees and I thought they may be Processionary Caterpillars but they don't seem to match the photos of those online nor the time of year when they are out and about ... There are loads in the pool again this morning and I've never seen caterpillars move so fast across the patio - they really are super speedy. It's strange that I cannot find it in my books that I have - normally they are a great help in pinpointing which caterpillar is which ...

Looks similar to the White Satin moth caterpillar?

Hi Longleaf - yes, just checked against some images on Google and it does look very similar but it's not the one! The White Satin moth seems to have double white spots rather than individual ones running down the back, and my one has white hair as opposed to a yellowish colour. But very close - perhaps a relative of the White Satin moth ...

Maybe Utetheisa pulchella (Crimson-speckled Moth)?

See 9th pic down on site:

http://www.leps.it/indexjs.htm?SpeciesPages/UtethPulch.htm

The larva seems to change pattern with age.

You sure have got us going on this caterpillar LOL, I spent an hour trying to find it but I didn't have any luck, maybe if you still have them crawling around you could try taking another picture, remember to half press your camera button half way down till it focuses and press it all the way down, if your already doing that way I expect your camera has given up the ghost LOL, if you did get a good pic then I would pop into your nearest garden centre & ask them about the little critter LOL.
Good Luck :o))

HEY! Hang on, I may have found it on Flickr......
I wonder if its this one???

Grey Dagger Moth Caterpillar (Aronicta Psi)

https://www.flickr.com/photos/rivercrouchwalker/7885673448/

Thank you Longleaf and Ladyessex1 - I have had a good look at both of your suggestions and I think we have a winner!!!!! I do believe I am being plagued by the Crimson Speckled Moth caterpillars - the 9th photo down on that link is almost identical!!!! And having now seen the photos of the moth itself I know that I have seen a lot of those flying around in recent years (but I've never seen these caterpillars before let alone a swarm of them) - they particularly like a large succulent-type bush with yellow flowers which mainly grows wild here but when some seeded in the garden I let it grow as nature intended. Thanks Ladyessex1 re camera advice - I've never been good with a camera so any tips are welcome! Thank you everyone for all your help - it's much appreciated. Nina PS - the caterpillars are still throwing themselves into the pool - how odd ....

Good to know you now have the name of the caterpillar.
Glad you liked my info re the taking pic's :o)) I used to just press the shutter button at one time but I now know better, its good to give advice so to help people, I now take pic's and enter them in Camera Club Competitions & have also received the Club Trophy Cup, with was such a surprise gotta give it back at the end of the season though, hopefully I'll win it back LOL. Jackie :o))