Instagram Model Erika Costell Smokin' Hot During Miami Beach Photo Shoot

Instagram model Erika Costell is living proof Jake Paul is one lucky bastard.

The YouTube star's alleged gf hit the water in Miami Beach Friday during what her friends say is an "impromptu photo shoot" ... but we're guessing this was well planned.

Erika showed off her smokin' bikini bod like a pro, including her tattoos -- mostly her "Fear Ends Where Faith Begins" tat on her left hip.

She specializes in bikini and lingerie shoots ... and to that we say, well deserved.