The species bound, a swampland conjecture, suggests that the cutoff of quantum gravity in an effective field theory coupled to a number of light fields is significantly lower than the Planck scale. Notably, the species bound offers insights into the interior of the moduli space. In this talk, I will review recent progress in this direction (2303.13580,2212.10286). I will begin by introducing the notion of the species bound and then discuss constraints on its dependence on moduli. Additionally, I will explain the connection to black hole entropy, which serves as a
non-trivial check of the constraint.