CORPUS CHRISTI, Texas — The drug runners call it "el mosco," the mosquito, and one recent evening on the southern tip of Texas, a Predator B drone armed with cameras buzzed softly over the beach on South Padre Island and headed inland.
"We're going to get some bad guys tonight, I've got a feeling," said Scott Peterson, a U.S. Customs and Border Protection supervisory air interdiction agent. He watched the drone's live video feed in the Predator Ops room at Naval Air Station Corpus Christi, about 50 miles away.
As the unmanned plane flew up the winding Rio Grande, which forms the border with Mexico, Peterson fielded excited phone calls. One agent had seen known scouts for a Mexican cartel at a Dairy Queen, suggesting a load of drugs was coming through. Another called in the precise spot where the shipment would land.
Soon the drone's infrared camera picked up a man hauling bales of marijuana from an inflatable rubber boat into a minivan on the Texas side of the river. Then it spotted a second boat. Agents readied for a major bust.
But the April 18 raid was not the success Peterson had envisioned. He wanted the drone to track the smugglers to a stash house, and perhaps to ranking cartel members. Instead, Border Patrol agents rushed to the riverbank, sirens blaring. They seized half a ton of pot, a 1996 Plymouth Voyager van and a boat. The smugglers escaped and no one was arrested.
The mixed results highlight a glaring problem for Homeland Security officials who have spent six years and more than $250 million building the nation's largest fleet of domestic surveillance drones: The nine Predators that help police America's borders have yet to prove very useful in stopping contraband or illegal immigrants.
The border drones require an hour of maintenance for every hour they fly, cost more to operate than anticipated, and are frequently grounded by rain or other bad weather, according to a draft audit of the program last month by the Homeland Security Department's inspector general.
Last year, the unmanned fleet flew barely half the number of flight hours that Customs and Border Protection had scheduled on the northern or southern borders, or over the Caribbean, according to the audit.
And the drones often are unavailable to assist border agents because Homeland Security officials have lent the aircraft to the FBI, Texas Rangers and other government agencies for law enforcement, disaster relief and other uses.
The audit slammed Homeland Security for buying two drones last year and ordering an additional $20.5-million Predator B system in Cocoa Beach, Fla., this year, saying it already owns more drones than it can utilize. Each drone costs about $3,000 an hour to fly.
"The big problem is that they are more expensive than traditional methods" of patrolling, said T.J. Bonner, former president of the National Border Patrol Council, a union of border agents.
To help pay for the drones, Customs and Border Protection has raided budgets of its manned aircraft. One result: Flight hours were cut by 10% for the P-3 Orion maritime surveillance planes that hunt smuggling ships on the West Coast and in the Caribbean.
The amount of illicit drugs seized in Predator raids is "not impressive," acknowledged Michael Kostelnik, a retired Air Force major general who heads the office that supervises the drones.
Last year, the nine border drones helped find 7,600 pounds of marijuana, valued at $19.3 million. The 14 manned P-3 Orions helped intercept 148,000 pounds of cocaine valued at $2.8 billion.
In an interview, Kostelnik dismissed criticism of the border drones as shortsighted. He sketched out scenarios, such as a nuclear plant meltdown or detonation of a dirty bomb, where the drones could help assess damage without endangering a pilot.
If a major terrorist attack occurred in Washington or New York City, Kostelnik said, he could put drones overhead in five hours, assuming they could be flown up from Florida or carried on a cargo plane, to help first responders and policymakers.
"It is not about the things we are doing today," Kostelnik said. "It is about the things we might be able to do."
The recent raid on the Rio Grande showed some of the pros and cons of the border drones.
Inside the Predator Ops center, the crew watched as the minivan filled with marijuana drove away on a dirt road. The Predator's camera followed. Suddenly, a figure raced in front of the minivan, waving his hands for the driver to turn back.
"He's spooked!" said Lyle Belew, the mission commander. "Stay on him!" he ordered the camera operator as the van did a quick U-turn.
Instead of risking a potentially violent standoff in a nearby residential neighborhood, the agents on the ground decided to cut the operation short and try to seize the drugs at the river.
A Border Patrol SUV suddenly appeared on screen, chasing the minivan back to the riverbank. Then six figures jumped out of the minivan and into the water, taking one of the two rubber boats. Several Border Patrol agents ran down the beach in pursuit.
In the Ops Center, Border Patrol liaison Hector Black worried that cartel gunmen might open fire on his agents from the far side of the river.
"Ask them to pan [the drone camera] to Mexico to make sure nobody starts shooting at our guys," Black said. "See if there are guys with long arms," meaning rifles.
The banks looked empty, but the camera clearly showed six figures and a rubber boat drifting down the dark river and back into Mexico.