  The chiral magnet Cu$_{2}$OSeO$_{3}$ hosts a skyrmion lattice, that may be
equivalently described as a superposition of plane waves or lattice of
particle-like topological objects. A thermal gradient may break up the skyrmion
lattice and induce rotating domains raising the question which of these
scenarios better describes the violent dynamics at the domain boundaries. Here
we show that in an inhomogeneous temperature gradient caused by illumination in
a Lorentz Transmission Electron Microscope different parts of the skyrmion
lattice can be set into motion with different angular velocities. Tracking the
time dependence we show that the constant rearrangement of domain walls is
governed by dynamic 5-7 defects arranging into lines. An analysis of the
associated defect density is described by Frank's equation and agrees well with
classical 2D-Monte Carlo simulations. Fluctuations of boundaries show
surge-like rearrangement of skyrmion clusters driven by defect rearrangement
consistent with simulations treating skyrmions as point particles. Our findings
underline the particle character of the skyrmion.
