  We analyse particle species and the species scale in quantum gravity from a
thermodynamic perspective. In close analogy to black hole thermodynamics, we
propose that particle species own an entropy and a temperature, which is
determined by the species scale. This is identical to the Bekenstein-Hawking
entropy of a corresponding minimal black hole and agrees with the number of
species in a given tower of states. Through the species entropy, we find that
certain entropy bounds are connected to recent swampland constraints. Moreover,
the concept of species entropy and temperature allow us to formulate the laws
of species thermodynamics, which are argued to govern the variations of moduli
in string theory. They can be viewed as general rules that imply certain
swampland conjectures, and vice versa.
