"They're from South America," said Syeda Jafri, spokeswoman for the Rialto Unified School District. "How they got here, we have no idea."
The school called in exterminators, and Jafri said the fields are expected to be clear of the unwanted guests by Friday, ready for next week's football game.
The infestation is not to be taken lightly, said Les Greenberg, an entomologist at the University of California, Riverside.
"A small percentage of the population is allergic to the venom, just as with bees or wasps," Greenberg said. "This could range anywhere from a nuisance to a health threat."
