  The Hofstadter butterfly spectral patterns of lattice electrons in an
external magnetic field yield some of the most beguiling images in physics.
Here we explore the magneto-electronic spectra of systems with moire spatial
patterns, concentrating on the case of twisted bilayer graphene. Because
long-period spatial patterns are accurately formed at small twist angles,
fractal butterfly spectra and associated magneto-transport and
magneto-mechanical anomalies emerge at accessible magnetic field strengths.
