Armed with a small flashlight, tweezers and knee pads, Tim Morris climbed into a cargo container at the port of Baltimore and slid along racks of aluminum sheets from China.
As an agricultural specialist for U.S. Customs and Border Protection, Morris was looking for any sign of wood-boring insects in the packing material around the racks. But more broadly, he was watching for a host of Chinese insect and plant species considered invasive threats to U.S. ecosystems and agriculture.
Within minutes, he'd spotted tiny borings and a single hairy seed, which he quickly collected with the tweezers and placed in a glass vial.
The seed, Morris said, produces phragmites, large reeds that have established themselves in parts of the country but are considered invasive in Maryland and a threat to the state's native cattails.
"It kind of chokes out marshes and is really ruining wetland areas in the state," Morris said.
Each day at the port of Baltimore, CBP officers serve as the nation's front line against a range of threats, including invasive species, illicit drugs and terrorism. They do similar work at BWI Thurgood Marshall Airport, screening international travelers, luggage and cargo.
Such federal workers are considered essential to the country's safety, as was made clear last month as Congress battled over funding for the Department of Homeland Security.
The department would have run out of money if Republicans and Democrats had not been able to work out a deal. Morris and other workers deemed essential would still have been required to report for duty but would not have been paid.
Morris said it is "always good to not have to worry about" getting paid and instead focus on the job.
CBP officers are charged with enforcing hundreds of regulations from about 40 government agencies, said Officer Robert Hunt, program manager at the Baltimore field office.
The rules cover all sorts of commodities and products, from automobiles — Baltimore handles more automobiles than any other port in the country — to food and building materials.
With McCormick & Co. and other spice companies in its backyard, for example, Baltimore imports huge amounts of spices from all over the world, including India, Egypt and Syria. Beetles sometimes ride along.
The port has long handled ceramic tiles from Italy, though China has recently begun pushing into that market. Slugs sometimes stick to the tiles.
Threats can come from anywhere in the world, and can mean substantial loses for critical industries. Pests can cripple agriculture. Counterfeit goods can undermine products and businesses.
"We're not just looking for insects. We're trying to save the U.S. taxpayers a ton of money, too," said Steve Sapp, a Customs and Border Protection spokesman.
About 220,000 cargo containers were imported through the port of Baltimore in 2014, officials said. Hunt declined to say what percentage is inspected manually, but said many are — by specialists such as Morris and other CBP officers.
Hunt said officers also use an X-ray machine to scan containers for anomalies, such as a duffel bag in a container of boxed goods. If something is spotted, it undergoes closer inspection.
Officers must keep abreast of the laws and regulations they are enforcing.
"Every day is school," said Dametrika Williams, a former corrections officer in North Carolina. "It's good because you don't get a chance to get bored."
On a recent morning, Williams used deadbolt cutters to snap the seal off a container labeled as holding boxes of dried apples from Chile.
An X-ray had shown an anomaly: Every layer of boxes appeared dark black in the X-ray images — an indicator of their density — except the top layer, which was substantially lighter.
The likely reason became clear almost as soon as the doors of the container were opened. All of the layers except the top layer, which had gaps, had boxes stacked in rows filling the width of the container. Agents opened a few boxes to make sure they were filled with apples, but soon closed the container with a new seal, indicating that the CBP had been inside.
In December 2013, officers at the port spotted two duffel bags on X-rays of a shipping container carrying auto parts arriving from Panama. They opened it and found 128 pounds of cocaine, worth an estimated $4 million on the streets of Baltimore.
In 2007, about 310 pounds of cocaine were found in three duffel bags inside a refrigerated container arriving from Ecuador.
If Williams or Morris find big problems with a container, it is sent to CBP's nearby Centralized Examination Station, they said.
There, cargo can be removed from containers for more thorough checks. Wooden packing slats can be chopped open by agents looking for wood-boring bugs. Entire loads can be vacuumed, so every seed can be captured before it can fly off a truck to who knows where.
Sometimes, entire cargo loads are rejected — requiring owners to send them back or dispose of them, usually through incineration.
If drugs had been found in one box of dried apples, every box would have to be opened, Hunt said, no matter how many there were.
On an average day in 2014, CBP officers at the nation's 328 ports of entry screened more than 1 million passengers, inspected more than 70,000 truck, rail and sea containers, seized more than 1,800 pounds of illegal drugs, and stopped more than 4,000 prohibited plant and animal products and 425 agricultural pests and diseases, according to Customs and Border Protection statistics.
Morris, who graduated from Virginia Tech with a forestry degree and started working for CBP a decade ago, said it's all in a day's work in Baltimore.
"If it's on a list," he said, "I'm concerned about it."