# Why does pair production only occur in an electric but not a magnetic field?

I recently read that the photon "decay" (if you can call it that) in an external field occurs only in an electric field but not in a magnetic field. The reason being that the Euler-Heisenberg Lagrangian is real-valued for the magnetic field whereas it has a non-vanishing imaginary part in the case of an electric field (the calculation is quite lengthy, so I won't repeat it here). That explanation is great, but I was wondering if there is also an intuitive physical reason why photons only produce $$e^- e^+$$-pairs in an electric field?

I find this effect quite fascinating as electric fields and magnetic fields usually behave so similarly. After all, you can change from one to the other by a simple Lorentz boost (at least to some extent).