  We study good, bad and not-even-bad diquarks on the lattice in a
gauge-invariant formalism in full QCD. We establish their spectral masses with
short extrapolations to the physical point, observing agreement with
phenomenological expectations. We find that only the good diquark has
attractive quark-quark spatial correlations, with spherical shape and size
$\sim0.6$ fm. Our results provide quantitative support for modelling the
low-lying baryon spectrum using good light diquark effective degrees of
freedom.
