updated 9:26 p.m. ET Sept. 24, 2008

RIALTO, Calif. - They’re a relentless force on the gridiron, with a stinging defense. But don’t expect anyone to cheer for the Rialto High School fire ants.

Discovered by a groundskeeper last week, the venomous red pests have set up several mound-like colonies on the football and baseball fields. The Southern California school canceled a freshman football game, moved practices and called the state Department of Agriculture.

“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.”

MORE FROM OTHER SPORTS

Other sports Section Front

The most important black athlete in existence the Grio: 100 black history-makers in the making Andrews stalker had 16 other victims, feds say 17 years later, Jones and Hopkins to fight again Roddick’s wife on cover of SI swimsuit issue   Video: SI's swimsuit issue is big business Pac-10 giving ‘serious evaluation’ to expansion Riley, Conradt on Hall of Fame Board of Governors Globetrotters play game on ice rink in New York Afghanistan hopes to defeat America - in cricket Other sports Section Front   Add Other sports headlines to your news reader: