The incident took place last Thursday aboard Flight 6316 from San Jose to Madrid.
The pilot told the Barajas control tower that a scorpion had stung a passenger; the airport's medical service was subsequently notified, the sources told EFE Monday.
Upon the airliner's arrival at Madrid, Barajas doctors confirmed the arachnid sting on the passenger's left arm, for which they took her to a hospital in the Spanish capital.
The woman of Swiss nationality remained under observation until she was released the next day.
The passenger was on a flight from San Jose to Madrid with another five people, who had planned to continue their trip to Zurich.
One member of the group remained in Madrid to accompany the passenger during her hospitalization, while the other four continued on to the Swiss city as planned.
The Iberia plane had to be sealed off, according to the regulations for such cases, in order to find the scorpion and disinfect the aircraft.