Rotor blades and methods for joining blade components of rotor blades are provided. A method includes positioning an insert between and in contact with a first blade component and a second blade component. At least one of the first blade component or the second blade component includes a thermoplastic resin. The insert includes a thermoplastic resin and an energy absorptive pigment. The method further includes heating the thermoplastic resin of the at least one of the first blade component or the second blade component and the thermoplastic resin of the insert. The method further includes cooling the thermoplastic resin of the at least one of the first blade component or the second blade component and the thermoplastic resin of the insert. The heating step and the cooling step join the first blade component, the second blade component and the insert together.