During flight, natural fliers flap, twist and bend their wings to enhance flight performance. Lift and thrust benefit from flexibility as well as from both passive and active wing deformation. At the same time, the active deformations are used for flight control. In this study, we investigate strategies of control moments generation in a bio-inspired flapping-wing micro air vehicle (FWMAV). In particular, we propose a method for active control and attitude stabilization by introducing a wing deformation through adjustable wing sweep. The control method is demonstrated on a tailless FWMAV with independent wing sweep modulation on each of its four wings. The actuation mechanism consists of an arm joint at the leading edge, about which the wings are swept. Forces from the servo actuation are transferred to the leading edge of the robot through strings. The actuated strings alter the wing sweep, which affects the roll and pitch movement via different combinations of string pulls. The effectiveness of the designed mechanism is being evaluated on the basis of tethered force balance tests and free flight tests. An advantage of the proposed mechanism is its lightweight design, which is crucial for small FWMAVs with stringent weight restrictions.