In the darkness of the night, a band of blue light flows through the waves rushing to shore, dispersing the glow like glitter. In the forest, too, there are lights: yellow pinpricks on a dark horizon. 

Witnessing bioluminescence—the phenomenon where certain species emit light from their bodies—can be one of the most striking encounters in nature. The animals, plants, fungi or bacteria with this spectacular trait create light through a chemical reaction, usually between oxygen and enzymes known as luciferin or luciferase, stemming from the Latin word for “light bearer.” One species of glowing algae, Noctiluca scintillans (meaning “night-shining light” in Latin), is often called “sea sparkle.” When a wave breaks on the shore, oxygen disperses, and the algae suspended in the water take on their unearthly glow. The reaction appears almost instantly.  

While most creatures capable of bioluminescence live in the ocean, some, like fireflies, live on land. When the summer sun dips and the chorus of birdsong settles, fireflies (also known as lightning bugs) take to woodlands and wetlands to reproduce. For some species, the twinkling lights of the males help the females determine their best mates, while the larvae (known as glow worms) use their light as a deterrent for predators. 

Though these light shows are often fleeting and rare, they can be found almost everywhere in the world and all shine brightest during the warmer months. Aquatic glows can be seen on the southern California coastline, the coasts of Wales and southwestern England, the Netherlands, Vietnam and Taiwan’s Matsu Islands. Terrestrial lights from fireflies and glow worms, among other species, thrive where habitats remain intact: in forest thickets and wetlands across Europe, North America and Japan, and deep in the caves of Australia and New Zealand. In almost every place, however, these species are under threat—either due to nutrient runoffs that catalyze harmful algal blooms or habitat destruction, light pollution and pesticides. Witnessing bioluminescence, then, is not to be taken for granted.