Summer is here and the fireflies are out.
I've noticed that when fireflies glow, they are almost always flying upwards. You rarely see one start glowing while it is descending. I admit, I've never heard this question before. That's how female fireflies tell males of the different species apart, and know whether they should respond or not. Cecil's Mailbag is researched and written by members of the Straight Dope Science Advisory Board, Cecil's online auxiliary.