RIALTO -- Rialto High School's new football field has some unwanted visitors -- ants.

A grounds keeper disturbed several dirt mounds filled with colonies of red imported fire ants last week.

The affected area is now surrounded by an orange fence.

School officials said the ants are "not to be messed with."

"When they poke the skin they cause blisters and we are more careful for our students because if you have allergies to bee stings, it can be fatal," said Gloria Shaw of the Rialto Unified School District.

No students ever came in contact with the ants, which are native to South America.

The district quickly contained the area and notified parents.

The biggest inconvenience has been to the Rialto High Knight football team, which has been using the lower field for practice.

"The kids are disappointed, of course, because they want to play every chance they get," said Athletic Director Dan Williams.

The school's Cross-Country team, which typically uses the stadium track, has also been forced to find other places to run.

"They have us practicing here or going to different parks but it's just not the same as practicing here at home," Cross-Country runner Jose Uveda told KTLA.

Last Thursday's freshman football game had to be canceled because of the ants, however, future games were still on schedule. This is the first season in the new stadium.

Insecticide applied Tuesday was expected to work within 12 hours.

Once the ants are gone, the football team will return to the field October 3 to take on another challenger -- the unbeaten A.B. Miller football team.