Sara Lewis has managed to put herself in the center of a world of wonder by becoming a world expert on fireflies. Her obsession began in grad school, sitting in a backyard in North Carolina and watching the sparks light up around her. She wondered, “How do these creatures make light? Are they talking to each other? What happens when light goes out?” As a professor at Tufts University, Lewis has been lucky enough to answer some of those questions.
Part of the beauty of fireflies, aside from the patterns of light itself, is that they “so beautifully illuminate the creative improvisation of evolution.” They have been shaped by both natural selection and sexual selection.
Lewis and other scientists have made many new discoveries about these odd glowing creatures in last 20 years. A few remarkable facts about them:
- Fireflies are beetles.
- There are more than 2000 firefly species that have evolved very different courtship styles
- 150 million years ago they flew during the day and didn’t light up.
- In some species the females are flightless and light up to attract flying, unlit males.
- In other species only the males light up, and in yet others, both do.
- They light up by a tightly orchestrated chemical reaction, involving the wonderfully named luciferase
But, asks Lewis, how could lighting up have benefited early fireflies? It turns out that the light first originated in the larval stage of fireflies. Those larvae make nasty-tasting chemicals to protect themselves from predators. It seems that the lights first evolved as a warning — danger! Do not eat! Later, that same light system evolved to be a part of complex courtship rituals.
As adults they live for only a few weeks, and are “single-mindedly focused on sex — that is, spreading their genes into the next generation.” And they use their lights to do this, lighting up in extraordinary displays as they search for mates. Lewis is particularly taken by this idea: “The luminous displays are actually the silent love songs of male fireflies. They’re flying and flashing their hearts out. I still find it very romantic.”
In most species, as the males fly above, the females are down below and are very picky. If they like a male, they’ll flash their light back. They prefer males who give longer-lasting flashes. In a surprising twist, Lewis and her colleagues found that while mating the male deposits not just sperm, but also a nutrient-filled package they’ve named the “nuptial gift.” This is what the females are really looking for — the long flashes of light helps to predict which males can provide lots of nutrients.
There is also a dark side. For the most part, fireflies don’t get eaten because they manufacture toxins. However, one branch has lost its ability to produce this toxin. Extraordinarily, though, they will go out and attempt to prey on fireflies of other species — drinking their blood to obtain their toxins. “A firefly vampire brought to you by natural selection.”
Unfortunately many questions about fireflies might remain unanswered, Lewis reminds us, as “around the world firefly populations are blinking out.” This is mainly due to habitat loss and light pollution. She finishes by saying, “As we work together to craft a planetary future, I hope we can work together to keep these bright lights shining.”