A Long Island high schooler has been arrested after threatening a “massive” shooting at his school. After the 16-year-old Bellport High School student posted the threat to Instagram on Thursday, police said they began receiving 911 calls. The teen was identified and arrested that evening, authorities say. In a news release, Suffolk County District Attorney Raymond Tierney said investigators questioned the unnamed teen and searched his home, where no guns were found. “We take these threats seriously and will devote our resources to ensuring the safety of our children,” Tierney said. The teen is expected to be arraigned on Friday.