I urge everyone to bookmark that blog; it is always a fascinating tour of the weirder and wonderfuller places on our planet. And let me leave you with this simply jaw-dropping video of undulatus asperatus in action.
(A sunscreen with a physical block like titanium dioxide or zinc oxide can be applied last, after a serum or moisturizer.) Apply a serum next and, finally, moisturizer if you need it. Polis also recommends serums or sunscreens with moisturizers built in because they save time.
Facial serums are lighter, more gel-like products that absorb quickly. They are highly concentrated and provide both moisture and nutrients to the skin. A serum is not meant to replace your daily moisturizer.