Great shot kevbob! And no, they are not suffocating, unless he tightened the lid on because he thought the fireflies would turn macho and fight their way out.
Haven't seen fireflies in ages. One of my fondest memories as a young child were running through the firefly swarms that filled my grandparents' yard on warm summer nights.
You would not believe your eyes
If ten million fireflies
Lit up the world as I fell asleep
'Cause they'd fill the open air
And leave teardrops everywhere
You'd think me rude
But I would just stand and stare
Those aren't real fireflies unless maybe they are from Texas. I played with fireflies as a child in Illinois and they were not nearly that big. I never put them a jar though i just ran around with them, caught them, let them go, caught them again...
I lived near a conservation area on some chalk downland a few years ago, where there was a colony of glow worms. They're amazing things - the female beetle sits on a bit of grass, and her abdomen glows to attract the males.
I took a picture of one - I think it's also pretty evocative: glow worm