And, btw, thanks for posting this question. Our lightening bugs haven't arrived yet and I haven't even thought of them yet this year. Your poll reminded me they're coming and made me smile on this hot, dull Friday at work.
both - although I think "lightening bugs" is being used more to the exclusion of "fireflys" which I heard/used more when I was young - many moons ago!!!!
Wow, this poll surprised me. Is it a regional thing? I just heard the name "lightening bug" a few months ago on a show my dd was watching. We've always called them fireflies. Interesting!