Ventral view of male, showing light organs slightly more extensive than those of female:

Note also the obvious impressions on the abdominal sternites (segments) of the male. This is one character in the key for Photinus pyralis according to the Dillons (1). Of course, the flash is distinctive, and this individual was captured while flashing. Note, also, the white fluid under the thorax--I presume this is reflex bleeding, and that the secretion is toxic--Eisner describes the toxicity of this family (2).