Amphiphilic block copolymers autoassemble in water to form either dynamically active micelles or frozen particles at high surface tension. The dynamics of these systems is dominated by an individual process, which involves insertion - expulsion of copolymer chains, and a collective one, which involves fusion and fragmentation of proper micelles. The details of these mechanisms can drastically affect the micelles' morphology and some of their applications (drug delivery, template for mesoscopic structures, etc.). While fusion and fragmentation were found to be important in out-of-equilibrium kinetics such as sphere-to-rod transition, they were reported to be irrelevant at equilibrium by both theories and chain randomization experiments. We show, for the first time, that fusion and fragmentation do in fact take place at equilibrium in triblock copolymer micelles poly(ethylene oxide) poly(propylene oxide)-poly(ethylene oxide). This was achieved using a fluorescent technique, which probes the randomization of hydrophobic pyrene derivatives between micelles.