The legs don't grow back, though. All of the dragonflies I asked were going too fast to hear me. Either that or they were too busy to stop. But I often see them eating mosquitoes, midges, flies, gnats, and other small flying insects. First they slash a cut in your skin, then they sponge up the blood and eat it.
Flashing is their way of advertising that they are available.
Different species of fireflies have different codes that they use. This is a way of defending themselves. I sure don't. Io caterpillars have spines on them that contain venom. This can cause painful blistering if a spine pierces your skin.