The 68 year-old is said to have suffered anaphylactic shock in the incident at the eaterie in the municipality of Teulada-Moraira a short drive north of the holiday resort of Benidorm.
Paramedics tried to save her by performing CPR but she was pronounced dead at the scene.
A spokesman for the Civil Guard said: “Officers attended the restaurant where the incident occurred after a British woman aged 68 was stung by a wasp.
“She was being assisted by emergency medical responders on the restaurant terrace when they arrived.
“She was subsequently transferred to an ambulance where she died after going into cardiac arrest.
“A doctor certified her dead around 3pm local time.”
A source close to the inquiry added: “It appears she went into anaphylactic shock but it will be up to a forensic expert during an autopsy to confirm this.”
The tragedy happened around 2pm Monday afternoon.
A British woman who answered the phone at the sports bar and grill identified locally as the place where it had occurred said Monday evening: “I’m sorry but we’re not allowed to say anything.”