  We study massless cosmic strings which are one-dimensional objects moving
with the speed of light. Perturbations of velocities of test bodies and
anisotropy of cosmic microwave background generated by massless cosmic strings
are analysed. These phenomena are analogous to the string wake effect and the
Kaiser-Stebbins effect for standard (massive) cosmic strings. There are two
regimes depending on the energy $E$ of a massless string per unit length. At
low energies, $EG/c^4\ll 1$, massless and massive strings act similarly. At
high energies, $EG/c^4 \sim 1$, massless string effects are quite different.
Our work provides a method to describe different physical phenomena on
spacetimes of massless strings which take into account the presence of a
parabolic holonomy.
