Third-graders released 72,000 ladybugs into the Mall of America this week.

But it wasn't an accident. They were supposed to.

The ladybugs are being used as a natural way to get rid of the many aphids feeding on the 30,000 live plants housed in the fully enclosed shopping mall and entertainment complex in Bloomington, Minn., according to LiveScience.com.

Turns out, ladybugs are the natural enemy of aphids.

"Ladybugs are what I like to call, sort of a biological defense system," Lydell Newby, the Mall of America's senior manager of environmental services, told Minneapolis TV station KARE.

While some shoppers worry the bugs might fly onto their meals, a Mall of America spokesman says ladybugs spend most of their lives eating plants, not human food.

The Mall of America also converts fryer fat from its restaurants into biofuel for security vehicles, and uses passive solar heat from its 1.2 miles of skylights to heat the complex, according to the mall website.