A big word for a big ability – bioluminescence is the abiity of certain species to emit light after dark. Fireflies and glowworms, the larval form of a beetle, can do this – but many other species can emit light as well,  including fungi, sponges, corals, algae, hydroids, marine worms, crustaceans,  and mollusks.
 
This eerie glow and pulsating flashes of light are produced when a chemical in their tissues called luciferin is broken down by an enzyme called luciferase.

Back to fireflies – these insects are one of my favorite things about summer. I loved catching fireflies in jars and watching them flash their lights for a brief time before releasing them. Years later, I learned that the pulses of light they emit are messages to their mates! The lights are how they find each other after dark.
 
Fireflies seem to need old growth to live, so don’t expect to find them in brand new neighborhoods where vegetation has just been planted. (Also, don’t spray pesticides liberally if you want fireflies. They will be killed by these chemicals just like mosquitoes and other insect pests.)

At one time, people kept glowworms in jars so that they could read by their dim, greenish-yellow light!
 
The best places to look for bioluminescence are in meadows, on warm evenings in summer, when glowworms congregate and along the seashore in summer when thousands of planktonic bioluminescent protozoans and algae emit flashes of light when waves break on the shore.

Many deep-sea fish emit light in the darkness of the abyss. Each species has a unique pattern of lights, suggeting that they might aid mate recognition.

Bioluminescent fungi have been known since the time of Aristotle and are most common in rotting logs.

Now that the days are shorter, take the opportunity some warm evening after dark to venture outside. It’s possible you might find something glowing nearby!