because their populations are in decline. NoImpactMan has a report, linking to a story that says
Of the nearly 200 species of fireflies on this continent, only a few are urbanites.
“There’s two or three species in North America that seem to put up with what people do,” Lloyd says.
I remember as a child in the city putting a little grass in the bottom of a jar kept from year to year for that purpose, running after them in the dusk to catch them, watching them flash until I fell asleep and setting them free the next morning. I remember the joy of sharing that fun with my kids. It's deeply saddening to think my grandkids might not be able to find lightning bugs.
The photo above of fireflies/lightning bugs in a jar is from Flickr.