Ten people were hospitalized in Nicaragua after being attacked by a swarm of killer bees disturbed during cemetery cleaning ahead of the Day of the Dead festival, firefighters said Sunday.

Officials said the 10 people were treated for allergic reactions after the aggressive Africanized bees attacked when people sprucing up tombstones at a cemetery in Esteli on Saturday attempted to destroy their nests.

Africanized honey bees, or killer bees, are a highly aggressive hybrid bee which have taken root throughout the Americas since being introduced in Brazil during the 1950s.