"Before I got this job, I never knew how to read a map," Esteban said as we set out. "In Guam, where I'm from, you take a left at the broken-down car or the leaning palm tree. Now, my map book is the thing I read the most."

The first home we visited was a 9000-square-foot mansion in Rancho Pacifica. It looked more like a hotel than a private residence. After calling the owner up on an intercom, Esteban pointed out a few black pellets on the ground to his left. "That's bat guano," he said, matter-of-factly. I said I couldn't imagine a bat finding purchase anywhere on the mansion's exterior wall. "You have to understand that these are very small bats," Esteban explained. "They can hang from just about anywhere."

In the first attic we tried, Esteban found mouse droppings, which he described as "20 times smaller than rat droppings," but no sign of rats. No footprints in the attic dust, no chewing on the ducts, no grease marks, and no droppings 20 times the size of the mouse droppings around us. Outside, near one of three large air conditioners, Esteban spotted a dead field mouse. "Air-conditioning lines are highways to the attic," he said. Walking around the house, he showed me a few other ways in which mice might have entered the house -- pieces of chewed insulation, open ducts -- and then, at a pile of woodchips, paused.

"There," he said, "do you see that? Beside the insulation."

It took me three or four seconds to see a bit of pinkish cottony insulation among the woodchips. It didn't look especially remarkable, but Esteban kept pointing with his flashlight.

"You see it?" he asked. "A tail!"

It took me a few more seconds to realize, but yes, the tail of a dead mouse was wedged between the baseboard and the house's overhanging outer wall. I felt stupid -- the thing had been less than four feet away from my nose -- but the more Esteban pointed, the more I saw, and the more I saw, the more I wondered at how much I'd missed in the first place.

The mansion had hundreds of entrance points: little holes, big holes, uncovered cracks, unfinished fissures, jogs between points in the foundation. The owner might as well have put out a welcome mat for animals seeking rent-free residence. Esteban wrote up an estimate of what it would cost to plug up all the holes and presented it, and off we went. We hadn't found evidence of roof rats, but in Esteban's estimation, cases of roof-rat infestation in San Diego have doubled in just the past couple of years. He believes the population spike to be a direct result of the recent construction boom: Not only do these 21st-century rats have more houses to choose from, but the new residences are being built quickly, with more than a few corners cut. "Rats don't need to live in houses," Esteban told me. "There are plenty of sources of available food and water outside. But then you get a house like this last one -- and that was probably a $3 million home -- and see holes and cracks and points of entry all over the place. Why wouldn't rats live there?"

Our next stop was a much smaller house, in Clairemont. Hydrex had sealed the place years before, and there were no signs of further infestation. The traps Hydrex technicians had set in the attic sat in wait for unsuspecting rodents. A few years had gone by, but the peanut butter in them looked soft and tasty. Esteban explained that he uses peanut butter because it sticks on the trap, won't go bad, lasts a long time before biodegrading, and -- most importantly -- rats like it. (Cheese, I was surprised to learn, isn't at all effective; when Esteban sees cheese in traps, he knows they've been set by an amateur.)

Next, Esteban told me that it's a good idea to screw the traps into studs in the attic, to prevent caught, still-living rats from taking off with the unsecured traps, dying in some dark corner, and stinking up the entire house. "A dead rat'll give off a heavy stench for three to four weeks before it decomposes," Esteban said.

Hydrex's technicians like to set six traps per attic access, all around the opening. In other words, more than enough. Otherwise, a few rats get caught, and other, sealed-in rats start eating the trapped ones. "We've seen lots of evidence of cannibalism in rats," Esteban told me. "I guess once you seal them in, they can get pretty desperate."

Standard tools for a pest control technician include a drill, mirrors, a box of spring-loaded rat traps, a flashlight, gloves, sheet-metal screws, a staple gun, ladders, wire-cutters, quarter-inch hardware cloth, fix-all plaster, cement, mortar mix, and concrete patch. In preparing and sealing an attic, it's important to set the traps last, to avoid the risk of setting them off yourself after having set them for the rats. As Esteban showed me the successfully sealed attic, he wondered why the owner of the house had called Hydrex. But it turned out that her troubles involved rats outside the house.

The owner described rats scampering around the patio, crawling over each other, and dying in the swimming pool. "Some nights, it's quite a show," she deadpanned. But there was nothing Hydrex could do. "We can't seal your whole back yard," Esteban told her. "They'll still find ways to get in." Then pointed out the possible entry points: holes under fences, spaces between slats, thick bushes, power poles, and lines. In a crunch, the rats could simply climb over the fences themselves. The owner -- a dog-lover -- was left with the option of securing a rat-killing cat.

A week later, I accompanied Esteban and Zaludek to Oceanside. Our destination, they assured me, was a house that really did have a rat problem. Before the real work began, they showed me more telltale signs of a serious rat infestation. Rats blacken the places where they walk; the Oceanside home was covered with their grease stains. Next, they had me poke my head up into the attic and take a deep breath. The smell of rat musk isn't a horrible one, and it occurred to me that its purpose is to attract other rats. But the smell is unmistakable, earthy, and 100 percent animal.


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