Fireflies shot through the darkness like yellow sparks as Epifanio Mendoza reported for work recently at Teabow Farms. Except for a pale moon, there seemed to be no light for miles in the Frederick County countryside.

But inside the farm's bright office, Mendoza's boss, Larry Jarvis Jr., eyes ever so faintly red, had already punched in. They greeted each other, and Jarvis -- using Mendoza's nickname, "Epi" -- offered him some Krispy Kreme doughnuts laid out on a counter.

They wore identical uniforms with patches that read, "Teabow Farms," though Mendoza's shirttails flew loose and the cuffs of his dark blue pants were stuffed sloppily into his tall rubber boots. The clock read 3:30 a.m.

For the next 12 hours, the two men worked a punishing shift, sometimes side by side, sometimes at opposite ends of one of Maryland's largest dairy farms, but always separated by a cultural divide.

Mendoza, 27, a Mexican immigrant, knows more English than most Latinos at Teabow Farms, but not much. Jarvis, 41, knows more Spanish than the rest of his family, which owns the farm. But not much. Like those on other dairy farms in the region, however, the two represent the transformation of agricultural labor as growing numbers of Latin American immigrants replace local farmhands.

As Jarvis and Mendoza entered a barn to check on the animals' feed, black-and-white cows, with their big, rubbery-looking heads and goggle eyes, gave them a once-over.

"How much we give these guys yesterday? Twelve? Today let's give them 13," Jarvis said, referring to the tonnage poured into shallow troughs near the animals' pens.

Mendoza nodded and uttered a few words in English. Jarvis strung together a phrase or two in Spanish. "Barnyard Spanish," Jarvis calls it, enough to allow him to learn some details -- but not a lot -- about his crew.

Jarvis said he knows, for example, that Mendoza has a wife and three little girls in Mexico.

"No toros," Jarvis says, using the Spanish word for "bulls."

Mendoza grinned.

Jarvis also said he knows that Mendoza's eldest daughter is 7 years old and his youngest is 1. He knows that Mendoza's family last saw him in August 2004. He knows that Mendoza sends a good bit of his paycheck to his family. He knows that Mendoza is waiting for the paperwork to bring his family to the United States. He knows that Mendoza works 70 hours a week, hoping to someday own a farm just like Teabow.

But Jarvis said he also knows that that dream is increasingly out of reach -- and not just for newcomers. His family has assumed a huge debt -- he won't say how much -- to modernize its farm and stay competitive in an unforgiving business. Each year, more farms vanish in suburban sprawl.

"He'd be better off to save his money and go back to Mexico," Jarvis said, a thought he has never repeated to Mendoza. "Why burst a guy's bubble?"

The two men split up. Nearby, a Latino crew worked in the milk parlor. Their uniforms were flecked with manure. Droplets of milk clung to their faces.

Teabow Farms, about five miles north of Frederick, has a herd of 1,820 animals, of which 950 must be milked daily. There are 18 hired hands. Ten are Latino, most of whom do the milking in shifts three times a day. Some have experience in farming, but most do not. The workers receive $7 an hour to start and receive free housing in two mobile homes on the farm. They do not have health benefits. Many come from the same town in Mexico or El Salvador; workers often recruit their relatives.

Jimmy Stup, whose father bought the farm 40 years ago, said there used to be no shortage of high school students asking if they could help bale hay. Now, even farmers' children look elsewhere for work. After all, Stup wondered, who would prefer strenuous labor at a little more than minimum wage in summer's heat and winter's cold when better-paying office jobs with air conditioning are available?

"It used to be there'd be five, six or seven coming around. This year, we've had one so far," Stup said.

One of the youngsters who came around years ago was Jarvis. At first, he just watched his father, Larry Jarvis Sr., a farmhand with the Stups for 35 years. When Larry Jr. turned 13, he began working summers for the Stups, collecting $1.85 an hour to bale hay or milk cows.

Over the years, he got to know Melissa Stup, Jimmy's sister. They laid eyes on each other when he was about 8, and it was not love at first sight. "I just remember she was in a wagon coming up to the house and she stuck her tongue out at me," he said.

By high school, they were dating. Jarvis enlisted in the Army, and the couple married. Both returned to the farm after Jarvis left the military in 1990. After taking a course on working with Latinos, they went on to oversee a Spanish-speaking staff that has grown through the years.

"You cannot find white people who want do to manual labor. It's hours and pay," Jarvis said.

Stanley Fultz, the University of Maryland's extension agent in Frederick County, said the trend began about 10 years ago on the state's biggest farms. Now, even the smaller farms, with 200 cows, employ immigrants full time, he said. The extension held a "Spanish for Dairymen" seminar last year, a first for the county.

The language barrier poses problems, Jarvis said. Cows have gone lame that otherwise would have been saved if the farmhands had been able to convey warning signs in English, and the Jarvises feel the limits of their Spanish.

After splitting up from Jarvis, Mendoza cut his way with a flashlight through a dark maze of fences and outbuildings to a shed where feed is stored in huge piles.

Inside the shed were piles of chopped silage, sugar beet pellets and mineral supplements, all rank with a yeasty odor. Mendoza pulled a dipstick from the crankcase of a Case front loader, checked the oil and fired up its diesel engine. He repeated the steps with a red tractor and connected the tractor to a huge green machine that mixes the feed and nutrients.

Then Mendoza drove the front loader from stall to stall, pile to pile, scooping tons of feed and dumping them in the mixer. He was nimble at the controls, wheeling the vehicle into tight spaces with one hand and maneuvering the front loader's bucket with the other.

This is not what Mendoza's father had wanted him to do. In Spanish, Mendoza explained that his father, a dairy farmer, told him to become an engineer or something that would spare him from the sun and sweat of agriculture. But Mendoza, one of eight children, disliked school. He liked working with his hands and working with animals, even though his left arm has bent backward since the day a horse kicked him 16 years ago.

Mendoza quit school in the fifth grade to work for his father. He earned about 100 pesos -- or $10 -- a day until he came here about two years ago and discovered he could earn that much in an hour.

Mendoza also likes that when people ask where he works, they recognize the name Teabow Farms. His father, he said, has about 80 cows on 60 acres in Mexico.

After mixing the feed, Mendoza hopped in the tractor and tuned the radio to WFRE-AM, the "free country" station. He likes the music but also hopes to improve his English by listening to weather reports and the deejays. After a while, he switched to a Spanish station.

Halfway through the feeding of the cows, a hydraulic cable popped loose, spraying oil. Mendoza wiped the hose with a rag, reattached it and searched for Jarvis.

"Hay problema," Mendoza said. Then, in English: "Leaks oil."

Jarvis asked if the hydraulic cable moves a door on the feed mixer, pointing, repeating himself several times in English.

"No, when I move that," Mendoza said, pointing to a nozzle.

"When the sun comes up, we'll change the tractor," Jarvis said.

Mendoza stared. Jarvis tried again: "When the sol goes up, we'll change the tractor. We'll have to get some more oil."

Understanding the gist, Mendoza drove the tractor to a barn to replenish its hydraulic fluid.

It is a scene repeated throughout the day. When they fail to comprehend, they point or gesture. Though their foreign vocabularies are limited, they have learned many unusual words. Jarvis, for example, knows that gato means cat in Spanish but also means the hydraulic jack used to lift equipment.

After the sun rose the next day, Jarvis and Mendoza decided it was time to replace the tractor because its hydraulic cable had snapped again.

As Mendoza backed up a tractor to the feed-mixing machine, Jarvis knelt on the ground with a jack. Mendoza delicately lined up the coupling, and Jarvis dropped in a pin. Then Mendoza climbed down. He picked up a heavy drive shaft that supplies power from the tractor's engine to the farm machinery in tow. Waving off an offer of help from Jarvis, Mendoza dropped it into place.

"That thing's a beast," Jarvis said.

Then Mendoza held out his hand as if to give something to Jarvis. A greasy lump of paper towel tumbled into Jarvis's upturned palm. Mendoza grinned.

"Oh, he shows me love every day," Jarvis said, going along with the joke.

Mendoza climbed back into the cab.

"Okay?" Jarvis asked.

"Muchas gracias," Mendoza responded.

Driving back to the feed sheds, Mendoza turned on a Spanish radio station and looked across the fields, smiling in awe at the vast farm.

Arnulfo Rodriguez, who emigrated from Mexico, prepares to milk a cow. Workers at Teabow Farms start out earning $7 an hour and receive free housing but no health benefits. Larry Jarvis Jr.'s family owns Frederick County's Teabow Farms, one of Maryland's largest dairy farms, where 10 of the 18 hired hands are Latino. Melissa Jarvis and Larry Jarvis Jr., who took a course on working with Latinos, oversee a mostly Spanish-speaking staff that has grown over the years. At Teabow Farms, where 950 cows are milked daily, the owners sometimes face language challenges with the crew.