Many arguments indicate that in the presence of a large number of fields, local field theory must "break down" at a length scale that is parametrically larger than the Planck length, the so-called species scale.  Aiming to clarify what happens then, we analyze the 2->2 scattering amplitudes of gravitons and contrast calculable field-theoretic contributions with possible short-distance completions, such as string theory or Planck-scale strongly-coupled physics.  The comparison reveals the phenomenon of "high-spin onset" which we argue provides a diagnosis for the (in)applicability of local field theory.  Based on arXiv:2408.06440. (Online talk)