The port of entry in Nogales is the busiest in the nation for fruit and vegetable shipments, requiring a steady stream of watchful eyes to prevent unwanted hitchhikers from other countries.

U.S. Customs and Border Protection scientists such as Tracy Filippi inspect the produce for potentially devastating insects or pathogens that can spread in the United States.

"Right now we're in high produce season, lots of volume coming across," Filippi said. "We see regular garden variety fruits and vegetables like tomatoes, cucumbers, bell peppers, but we also see some specialty types of Asian bassicas or Asian cabbages, and those are looked at depending on the pest rate."

The Nogales port of entry processes tons of fruits and vegetables each year that are typically trucked to the United States.

Officers with Customs also deal with private-vehicle passengers in cars occasionally bringing prohibited or restricted items such as birds or presents from well-meaning family members south of the border.