Why do you want to take maggots to the Ebro? I've fished a few Spanish waters including the Ebro and your main quarries will be Catfish, Carp and perhaps Barbel (not sure if there are any in that river)so your main baits will be luncheon meat, sweetcorn or bread (which you can buy in any local shop)for the carp and dead baits for the moggies. If you use maggots you'll just get pestered by little fish called pumpkin seeds.
I made that mistake only once, never again.