So are you saying your glow-worm is our lightning bug ("Firefly")? our lightning bugs/fireflies are beetles and some fly/some dont. Depends on species and sometimes sex. And the different species here have different light patterns. It's amazing to camp in the middle of the forest in the summer, they light up in waves, the different light patterns syncing up and it's a symphony of light that goes on for hours with hundreds visible. I swear you could write music to their patterns. My understanding was the UK does not have lightning bugs so that's interesting you've found some, then? Are they actually native?
Our glow-worms are super tiny and look like grains of rice (or smaller), as they are larval Orfelia fultoni (a type of fly). Famous here are the Dismal Canyon ones, which are distantly related to the glow-worms in New Zealand. I think we may have other species, as the Dismal Canyon ones emit different colour than the ones I see in the caves as my eye sees them, but they are under-studied (and something I hope to study in future if I can get some grants).
You can find them in Sauta Cave here at the entrance, and also Neversink which is a popular night trip in the summer. I do not have a macro lens, so capturing their light is all I can do camera-wise - first is with some fill to see the setting, second is just their light. I have some others on flickr.
Log Glowworms - Fill Light by
Amata Hinkle, on Flickr
Log Glowworms - No Fill by
Amata Hinkle, on Flickr
And although a little harder to see without pixel-peeping you can see them in the dark areas on floor and wall:
Neversink on Rope with Glowworms by
Amata Hinkle, on Flickr