I present the main results of an observational programme of search and study of extended ionized nebulae around symbiotic Miras. These nebulae provide unique information on the occurrence, geometry and dynamics of ancient mass loss events from these systems, which are likely to be related to unrecorded outbursts of their hot components. From the kinematics of the nebulae, it appears clear that fast winds from the hot components play a basic role both in shaping the nebulae and in accelerating the circumstellar material to velocities which are one order of magnitude larger than a typical Mira wind. I set some constraints on the recurrence time between outbursts and the accretion rates of the hot components, using the observed high incidence of nebulae among symbiotic Miras, the observed multiple nebulae, and the maximum observed age of the nebulae. New results are presented for HM Sge, V1016 Cyg, CH Cyg, He 2-147, RX Pup and R Aqr, as well as new HST imaging of He 2-104.