By Lisa Maria Garza

BROWNSVILLE Texas (Reuters) – With binoculars in hand, an assault rifle slung over his chest and a Glock pistol on his hip, a man named Will scans the banks of the Rio Grande looking for anyone trying to cross from Mexico into Texas.

Will is a member of the Patriots, a group of heavily armed private citizens who use displays of force to intimidate people attempting to cross the border illegally. Since early summer the Patriots have patrolled an area near Brownsville, Texas.

"If you spot them and shine your light on them, that lets them know that you're there," said the 25-year-old construction worker from Indiana who flew to Texas for a stint with the Patriots. "Nine times out of 10, they're not going to come over.

"Even if they are going to try to cross again, we're still making it harder for them, and that's the reason we're here."

The Patriots Information Hotline, a networking call center, estimates that 22 groups of "armed patriots" have sprung up along the border from Texas to California this year.

With names like Patriots and Citizen Defenders, the groups often set up camp on private land along the border at a property owner’s invitation. Expenses are generally paid by members, though some funds come from like-minded donors.

To critics, they are militias – vigilantes spoiling for a fight. For would-be migrants, they are another barrier to entry. For the U.S. Border Patrol, they can be either a nuisance or a help in spotting people trying to enter the country illegally.

The groups insist that their presence is unrelated to the tens of thousands of children from Central America who flooded across the border with Mexico earlier this year. Law enforcement officials say an increase in people taking part in citizen patrols in border states coincided with the attention being paid to the issue of unaccompanied minors this year.

Despite an aversion to the media, the Patriots opened their Brownsville camp to Reuters this month for an exclusive visit, saying their efforts are essential because the U.S. government has failed to secure the border.

Sitting on camp chairs in the center of a cluster of tents, members asked to be identified only by their handles or first names. An American flag flew above a yellow banner depicting a rattlesnake, ready to strike, and the words "DONT (sic) TREAD ON ME."

The men bristled at the terms "militia" and "vigilante."

"Everybody has this bad taste in their mouth about ‘militias.' They think we're out here trying to smoke people and kill them as soon as they cross the border. Which obviously, is not the case," said "Huggie Bear," a 25-year-old former U.S. Army infantry team leader.

"Our goal here is to try to deter them from coming. They see us, they don't know who we are, so that kind of scares people away for a while."

BODY ARMOR AND HANDCUFFS

The Patriots operate on 21 acres of land owned by Rusty Monsees, whose family has had a ranch on the border since the 1940s. They patrol in body armor, riding all-terrain vehicles that drown out the sound of cicadas at night.

Monsees, 66, said "illegals" have poisoned his dogs and sprayed his yellow house with bullets, but he refuses to leave.

"If they leave, I'm dead," he said.

The Patriots carry plastic handcuffs to detain border crossers and communications equipment to inform Border Patrol.

The only live fire they have seen has come from a Border Patrol agent who fired at them.

Border Patrol said the agent saw an armed man and thought he was part of a group of migrants suspected of illegally crossing the Rio Grande. Several shots were fired at the Patriot, who immediately dropped his weapon and was not injured.

Some say it is just a matter of time before one of these groups sparks a deadly firefight along the border.

Eddie Guerra, sheriff of the Texas border county of Hidalgo, is concerned.

"When there are situations with any individual who is bearing arms in public or on private property, there is always a concern amongst law enforcement of possible misidentification that can lead to friendly-fire tragedies," he said.

Border Patrol has warned the groups that taking matters into their own hands could have "disastrous personal and public safety consequences."

Over the weekend, President Barack Obama said he would delay an executive action on immigration reform until after November’s congressional elections, bowing to concerns that it could cost his fellow Democrats control of the U.S. Senate.

Many in Brownsville live in the shadow of an 18-foot-high rust-colored steel barrier that stretches hundreds of miles along the border. A few, including Fernando Rivera Jr., have called on groups like the Patriots to keep an eye on their properties.

"Whoever says there's not a problem by the border wall, they don't live out here," he said, adding that his son walks around the backyard with a shotgun slung over his back to protect the family from what he says are criminals coming across the border.

In addition to the Monsees property, the Patriots monitor homes in the area at the request of owners like Rivera, who said it can take up to 45 minutes for a county sheriff to arrive after a call for help.

"Now, when they're on patrol, it's actually peaceful," he said. "The dogs don't bark as much. I can actually get some sleep."

(Additional reporting by Jim Forsyth in San Antonio, Texas; Writing by Jon Herskovitz; Editing by Douglas Royalty)