I was wondering if we could ID male fireflies using their wavelength? A bit like how we use UV light to ID species of scorpions.
In short: Yes it should be possible, but probably not for all species and as @anongoodnurse said there are probably easier methods of species-identification.
I know (but could not find a reference) that there are currently hyperspectral cameras that are able to capture bandwidths as small as 2 nm.
And there are differences in the emission spectrum of fireflies. Firefly luciferase bioluminescence color can vary between yellow-green (λmax = 550 nm) to red (λmax = 620). ( https://www.ncbi.nlm.nih.gov/pubmed/2801227 ) There are currently several different mechanisms describing how the structure of luciferase affects the emission spectrum of the photon and effectively the color of light emitted. (https://en.m.wikipedia.org/wiki/Luciferase)
However, it is likely that there are closely related species of firefly that have no (or very small) differences in emission spectrum. These will not be identifyable with spectral imaging.