  We consider swarms formed by populations of self-propelled particles with
attractive long-range interactions. These swarms represent multistable
dynamical systems and can be found either in coherent traveling states or in an
incoherent oscillatory state where translational motion of the entire swarm is
absent. Under increasing the noise intensity, the coherent traveling state of
the swarms is destroyed and an abrupt transition to the oscillatory state takes
place.
