Dear WW: here is a link some of your kids might enjoy. It tells about how fireflies work:

http://www.discoverchemistry.com/dcv2-docroot/student/hot_topics/bioluminescence/default.html

I have seen fireflies many times, occasionally glow worms. In salt water, there are plankton and small jellyfishlike creatures that are a problem to navies, because they make so much light on dark night when disturbed by the ship's wake that the ship's location can be seen for many miles. Recently a Ukranian scientist was charged with betraying state secrets for publishing a paper about this!