Male adult railroad worm beetle!
The Phengodidae are beetles commonly known as glowworms. The adult females are wingless, larviform, and have light organs. The adult males, on the other hand, are small winged beetles with reduced elytra and feathery antennae, looking almost like a skinny clear-winged moth.
Most male phengodids don't glow, but there are a few exceptions. Males of the subtribe Mastinocerini actually retain the larval light organs on the abdominal segments, and the most famous of these is the genus Phrixothrix, the railroad worm, named for the paired light-organs on each segment of the larvae and adult female. Like the rest of the Mastinocerini, the male also has these lateral abdominal lights while lacking the cephalic light organs, the "headlights" of the train.
I've never actually seen an adult male railroad worm with his light organs glowing, but it's documented in multiple scientific papers, including one where they actually had male pupa hatch in captivity.
Sadly there’s no picture online of a male with his abdominal lights glowing. It’s attained an almost mythical allure for me. Perhaps one day...
The entire point of this essay was to explain and justify the above design.