Not 100% VC but I have raised the American variety of moon moth and the caterpillars looked rather similar to this, but I can't recall if they had the red pseudo legs or not. They are a world wide species, including Spain so the caterpillars will be different for each species I suppose..
A side on shot showing the whole caterpillar is the best to ID them, but I know that's not always possible. Hope this helps.
