Fireflies don’t see blue or red light very well because they have evolved to focus in on the particular yellow-green hue that they use to communicate. The brightness of the artificial light source makes a big difference, but its dominant color is also a factor. Radim Schreiber/Firefly Experience, CC BY-ND Previous research shows that female fireflies prefer bright flashes over dim ones, and background light can turn an otherwise bright flash into one that is dull and unimpressive.Ī female firefly signals. Or even if they do manage to pick out a male flash pattern here and there, they might not think it worth a reply. It may be that female fireflies are quite literally blinded by the light shining down into their eyes. Under artificial light, males flash about half as often, while females rarely, if ever, flash back. Our recent lab study shows that females of a common New England firefly species are even more sensitive to direct illumination than their male counterparts. He zips over, and that’s when the magic happens.
When a female sees a male she likes, she flashes back. As with most animals that engage in complex courtship rituals, female fireflies are the choosy ones – and they are watching the show with the rest of us.
Scientists have known for some time that direct illumination from a nearby streetlight makes male fireflies flash less, but that is only half the story. It doesn’t work so well with the lights on. The fundamental problem is visibility: Fireflies use their bioluminescence to flirt in the dark. More than a decade of scientific research offers ample evidence that light pollution is a threat to firefly reproduction. We and other firefly researchers have become increasingly worried about the future of these remarkable insects. Southeast, coordinate their flashes into bursts that ripple through groups of insects. Synchronous fireflies, native to the U.S. The more we light up the night, the less space we leave for the firefly flash dance. Humans can use curtains to block out a neighbor’s annoying LED floodlight, but nocturnal animals aren’t so fortunate. Human-caused light sources – house lights, path lights, streetlights – often shine all night, year-round. But as advances in technology made it cheaper and easier for humans to light up their environment, light pollution has become a constant presence in urban, suburban and rural habitats.
Females, perched in the undergrowth, discreetly respond when they are interested with flashes of their own.įor the vast majority of evolutionary history, nighttime light sources were predictable and short-lived: The sun set, and the moon waned. The males fly around, producing a species-specific pattern of flashes. Each evening, males and females engage in a dash of light flirtation. Most North American species have a two- to four-week mating season. Here in North America, nearly 150 different species of flashing firefly light up our summer nights.įind other ways to listen to The Conversation Weekly podcast here. Today, most glowing watches use a radioactive isotope of hydrogen called tritium (which has a half-life of 12 years) or promethium, a man-made radioactive element with a half-life of around three years.Fireflies evolved some 100 million years ago and have blossomed into more than 2,200 species that are found on every continent except Antarctica. In the past, the radioactive element was radium, which has a half-life of 1600 years. In these products, the phosphor is mixed with a radioactive element, and the radioactive emissions (see How Nuclear Radiation Works) energize the phosphor continuously. The most common place is on the hands of expensive watches. Occasionally you will see something glowing but it does not need charging. The phosphor is mixed into a plastic and molded to make most glow-in-the-dark stuff. It has a much longer persistence than Zinc Sulfide does.
Strontium Aluminate is newer - it's what you see in the "super" glow-in-the-dark toys. Two phosphors that have these properties are Zinc Sulfide and Strontium Aluminate. To make a glow-in-the-dark toy, what you want is a phosphor that is energized by normal light and that has a very long persistence.