It's not just insects. On his desk, Ng displayed some huge, beautifully colored snail shells that had been seized coming into Baltimore as live specimens. They were from the African land snail, a ferocious plant-eater that caused considerable damage after a mother in Miami threw out her child's three pet gastropods. Ng said some people try to bring them into the country expecting to cook up a meal of oversized escargot.

Customs inspectors are also looking for products that could spread diseases among humans and livestock. Among the seized products that Ng noted was a bag of yak jerky seized because it came from an Asian country where cattle are known to have hoof-and-mouth disease. Then there was a canned steak and kidney pie from Britain, confiscated because of concerns about mad cow disease in that country.

"If I weren't in this job, I wouldn't think much of it," Ng said. "It's cooked, it's processed. It's canned."

The customs agency, part of the Department of Homeland Security, has several offices around the port of Baltimore and at BWI Marshall Airport.

Customs isn't just looking at imports intended for sale on U.S. markets. The agency oversees the proper disposal of garbage from cruise ships and airliners, which can bring unwanted items in, Ng said.

Inspectors also pay attention to the materials in which products are packaged. Ng said dangerous snails can attach themselves to containers, while wood-boring insects can get into the country in the wooden shipping materials used for many products.

At the port, Ng opened a container with dozens of pallets of granite slabs. He examined the wooden packing material and saw it had a brand mark showing its had been chemically treated for pest resistance. Seeing no signs of sawdust or other clues of wood-borer activity, and finding no signs of pests "hitchhiking" on the granite, he cleared the shipment for import.

The inspectors don't check every package or even every shipment. There's not enough time in the day. Rather they depend on advisories from other ports, experience and the track records of individual importers to decide which items require a random check. Visual inspection is the No. 1 tool, but if they suspect there may be prohibited items deep in a shipment, they can use X-rays to investigate.

The customs inspectors work closely with federal agencies such as the Centers for Disease Control, the Food and Drug Administration and the U.S. Department of Agriculture, as well as state agriculture officials.

Julie Oberg, a spokeswoman for the Maryland Department of Agriculture, said the customs agriculture specialists have been very helpful to her agency.

"They are the first line of defense to protect the state's most valuable industry: agriculture," she said. "Their findings help us to target our surveys and make them more effective."

Ng said some of the best interceptions of his career have come recently.

About two weeks ago, he said, he found longhorn beetle larvae among some rolls of aluminum coil. The recent Khapra beetle findings have been professionally satisfying, he said. Since the beginning of the federal budget year last October, he and his team have made 13 first-time interceptions of new pest species in Baltimore. Another seven couldn't be identified by species but are believed to have been new finds in the port.

"When we do find something, it's gratifying," Ng said. "It shows we need to stay on top of it, and stay aware and vigilant, and not become complacent, because we're continually finding new things."

Khapra beetle

Latin name: Trogoderma granarium

Adult size: 2-3 millimeters

Origin: India

Countries under U.S. quarantine include: Egypt, India, Israel,

Morocco, Pakistan, Saudi Arabia and Turkey.

Host environments: Grain and cereal products. Feeds on almost any dried

plant or animal matter, including dog food, dried orange pulp and bread.

Danger: Severe infestations can contaminate stored grain, making it unpalatable or unmarketable.

Treatment: Fumigation with methyl bromide

SOURCE: U.S. Department of Agriculture