  The minimal coupling of massless fermions to gravity does not allow for their
gravitational production solely based on the expansion of the Universe. We
argue that this changes in presence of realistic and potentially detectable
stochastic gravitational wave backgrounds. We compute the resulting energy
density of Weyl fermions at 1-loop using in--in formalism. If the initially
massless fermions eventually acquire mass, this mechanism can explain the dark
matter abundance in the Universe. Remarkably, it may be more efficient than
conventional gravitational production of superheavy fermions.
