  In the first 3.5 years of operations the Fermi LAT detected several sources
with daily fluxes brighter than F(E>100MeV) > 10^{-6} ph/cm^2/s, the threshold
set by the Fermi Collaboration for issuing an Astronomer Telegram. We focus the
attention on these flaring sources, most of which are blazars, known to be
extremely variable over the whole electromagnetic spectrum, from radio to
gamma-ray energies and we investigate the properties of the selected sample
comparing them to the general characteristics of the Fermi catalog sources.
