MCALLEN, Texas (Reuters) - Homeowner Cosme Liscano is fed up with the gangs in his neighborhood in this Texas town near the Mexican border.
"This has been going on for three or four years now, they've been selling drugs," Liscano, 55, told Reuters as he stood in front of his house as members of the local gang enforcement unit frisked several suspects.
As violence spirals across the border in Mexico, law enforcement officials on the U.S. side of the Rio Grande Valley in south Texas say they have not seen significant spillover.
But while American border towns have not seen anything remotely approaching the blood-stained carnage of some north Mexican cities where rival drug cartels are in a high-stakes war that killed over 6,000 people last year, criminal street and prison gangs have long been a way of life in south Texas.
And while the links they may have to the Mexican cartels are often murky there are concerns that the drug lords to the south can tap this ready-made criminal infrastructure for a range of nefarious purposes.
In semi-rural Hidalgo County which lies to the north of the Rio Grande River separating Texas and Mexico, Sheriff Guadalupe Trevino reckons that there are about two dozen hardcore gangs operating -- a staggering number for a county with about 750,000 people.
"We have a serious gang problem here and have for a long time ... I believe we have more gangs than any other county on the border," Trevino told Reuters.
The extent of the problem -- the gangs often keep their fighting among themselves -- is hard to comprehend driving past citrus orchards or down the busy roads leading to the border. Some of the towns here are among the safest in the country.
But driving in poor, run-down neighborhoods in an unmarked SUV, heavily armed members of Trevino's elite gang enforcement unit point out gang graffiti scrawled on the sides of ramshackle homes. "Brown Pride" and "Tri-City Bombers" are among the many gangs competing for local turf.
The unit pulls over one heavily tattooed and shabbily dressed young man walking with a limp. It transpires that he has a small amount of marijuana on him in violation of his parole and so he is arrested, cuffed and put in the SUV. The limp is from an old gunshot wound.
"He says he's not a gang member but look at those tattoos," says one member of the unit, who can read affiliation in the elaborate tattoos. The young man's occupation is listed as field worker, a low-wage and physically hard job that probably makes gang work attractive.
Gangs and their culture of violence, drugs and crime are one of America's pressing social ills. But in the borderlands the problem has an urgency that has federal investigators worried.
"In the United States the local gangs play a major role in the distribution of the drugs brought in from Mexico. In southern California there has been significant cooperation between the drug cartels and the gangs there," said Matthew J. Desarno, acting unit chief of the Safe Streets and Gang Unit at Federal Bureau of Investigation headquarters.
"We believe that the gangs in Texas are following that (southern California) model to establish links with the cartels to expand their own business operations ... Gang members will do what is profitable," he told Reuters by phone.
In other small border towns such as Douglas in Arizona, hardened gangs from Los Angeles are carving out turf as part of a scramble to make money from the tons of illegal drugs pouring north from Mexico each month.
Investigators and police say cross-border links between the cartels and gangs face one obstacle more formidable than the Rio Grande River: trust.
The cartels will deal with the U.S. gangs on some levels but there are clear lines in the sand. Business stays in the family.
"The gangs are a resource for them but not their primary resource. I've been working this for 37 years and the Mexican drug dealer is a very parochial individual. He will rather deal with a family member than someone just entering the business," said Sheriff Trevino.
The FBI's Desarno says for example that the Mexican drug lords would not entrust an American gang with the task of bringing large quantities of cash -- the profits of their trade -- back to Mexico.
But there are worrying signs of cross-border cooperation.
A live hand grenade traced back to a Mexican cartel stash was tossed onto the pool table of a bar frequented by off-duty police officers in January in the Hidalgo town of Pharr. The pin was left in it apparently by mistake so it did not go off.
"That grenade shows there is some sort of association between one of our local gangs and the Mexican cartels," said Sheriff Trevino -- though he said the extent remained unclear.
One thing that is also clear is that the cartels are running a lot of drugs up through this neck of Texas.
At the Hidalgo County Sheriff's Annex building in the town of Edinburg roughly 4,000 pounds of seized marijuana and other drugs lie stacked in tight bundles. They represent hauls from several different operations and seizures and would have a street price of millions of dollars.
"All of this is from Mexico," said Sargeant Aaron Moreno, the head of the gang enforcement unit, as he pointed to the bundles which emitted a heavy and pungent odor.
Editing by Cynthia Osterman