  The dispersion relations of magnons in ferromagnetic pyrochlores with
Dzyaloshinskii-Moriya interaction is shown to possess Weyl points, i.\,e.,
pairs of topological nontrivial crossings of two magnon branches with opposite
topological charge. As a consequence of their topological nature, their
projections onto a surface are connected by magnon arcs, thereby resembling
closely Fermi arcs of electronic Weyl semimetals. On top of this, the positions
of the Weyl points in reciprocal space can be tuned widely by an external
magnetic field: rotated within the surface plane, the Weyl points and magnon
arcs are rotated as well; tilting the magnetic field out-of-plane shifts the
Weyl points toward the center $\bar{\Gamma}$ of the surface Brillouin zone. The
theory is valid for the class of ferromagnetic pyrochlores, i.\,e.,
three-dimensional extensions of topological magnon insulators on kagome
lattices. In this Letter, we focus on the $(111)$ surface, identify candidates
of established ferromagnetic pyrochlores which apply to the considered spin
model, and suggest experiments for the detection of the topological features.
