Try checking 1 billion fresh cut flowers for pests and diseases for Valentine’s Day.

That has been the job of dozens of agents for the U.S. Custom and Border Protection in the last few weeks leading up to Feb. 14, one of the busiest flower-selling days of the year.

At ports around the country, CBP agents have been working “extremely hard to make sure flowers get to businesses and homes around the country in time for the big day, but they’re doing so in a way that ensures the American environment and economy is protected," according to a statement from Kevin Harriger, CBP’s executive director for the agriculture programs and trade liaison office.

Experts said flowers that are imported can carry what’s known as “hitchhiking pests and diseases” that can cause millions of dollars in damage to the U.S. flower industry. Most flowers are safe, but even “one hitchhiking pest or plant disease could cause significant damage to American agriculture,” experts from CBP said.

And pests do get caught.

In this flower season, more than 1,660 pests were caught from nearly 1 billion flowers at some of the country’s busiest ports, according to CBP. Some of the pests that were caught included spider mites and cutworm moths. Most of the roses and mixed bouquets of flowers that are shipped to the United States come from Mexico, Colombia and Ecuador.

Once pests and diseases are found, officials said, they can treat some flowers and release them but may have to send some back to where they came from or destroy them.

The agency thanked its agents in the field on Twitter, saying “It’s #ValentinesDay, and we just want to say, thank you to our crew, for making sure no pests got through.”