We use Kepler light curves of G, K and M type stars to study the occurrence of superflares with energies above 5x10^34 erg. From the 117661 stars 380 show superflares with a total of 1690 such events. We determine which conditions are favorable for their occurrence, like the star's temperature and rotation rate. From that analysis we find that the flaring rate increases with the non-dimensionalized rotation rate, the inverse Rossby number, up to a critical point. This is expected from standard dynamo theory where the magnetic activity is enhanced by rotation or shear. At the same time we observe an increase of average flare energy with Rossby number which suggests an increase in spot group area. Using a standard alpha-Omega dynamo model we perform simulations of magnetic field amplification with different magnitudes of shear and confirm the positive correlation between rotation rate and magnetic energy dissipation.