I can see them hovering in my Brooklyn yard: tiny balls of yellow light that flicker on and off in the dusk like lighters at a rock concert.
Fireflies are quite a common sight, although for how long we don't know. There have been widespread reports that firefly numbers are dwindling. The reports are all anecdotal, but they were enough of a concern for entomologists and biologists to hold a symposium in Thailand in 2008 entitled, "Diversity and Conservation of Fireflies." If fireflies are under threat, it's a terrible state of affairs.
Fireflies belong to a very exclusive group of land creatures that exhibit a phenomenon known as bioluminescence.