One half of the Island Boys got locked up right before the new year started … and now we have a better idea why.

TMZ broke the news … Franky Venegas was arrested again in Florida for alleged drug-related offenses and is currently behind bars.

According to a sheriff’s report we just obtained … Franky and his female companion were pulled over for a routine traffic stop … and were allegedly acting super suspicious.

Deputies searched the car, per the report … and allegedly found unprescribed Zolpidem tartrate — basically Ambien — in a baggy with other pills that were prescribed to the woman. Deputies also allegedly found drug paraphernalia that tested positive for fentanyl — including Franky’s debit card, which allegedly was coated in white powder that tested positive for fentanyl, and a cut straw.

Franky was booked into the Collier County Jail in Naples Wednesday night on one count of drug paraphernalia, posing for a fresh mug shot … face tattoos and all. The woman was booked for the Zolpidem tartrate since there was no prescription.

As we reported … Franky had no bond, as he was on a hold since he’s already out on bond from a February arrest for delivering/possessing/selling a firearm with an altered serial number.

Franky rose to fame in 2021 with brother Alex after their viral hit, “I’m an Island Boy.”

He’s previously been arrested for domestic battery, reckless driving, and driving without a license.