This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Just as one insect mystery was solved, another appeared. In this case, it arrived under the wan light of the lunar eclipse last week. I was in rural western Kentucky visiting family and I had been impatiently checking to see if I could see the eclipse. Frustratingly, clouds that were patchy as the moon rose full and bright formed a gray wall as I knew the eclipse began.
As the time came for the moon to enter totality, I went outside again. Nothing. Minutes ticked by. The peak of the eclipse drew near. And at last, there it was – the full, dim eclipsed moon, hanging grimly like the Death Star. It was fabulous.
As I stood there, I noticed something else odd – the lawn seemed to have decorative lights. At first I thought they were fireflies that had momentarily landed. But as I continued to watch the moon, I realized that though they moved, they never flew. Were these the mythic “glow worms” I'd heard people talk about in the area when I was a kid?
On supporting science journalism
If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.
As I grabbed and seated myself in a lawn chair to savor my moon-viewing, I saw the lights were slowly moving. They seemed to me like a field full of wandering stars, or the headlights of cars driving along windy roads seen from an airplane high above.
I decided to discover the source of these mysterious lights. I shone the light from my phone screen onto one of the moving points, and sure enough, I could see something dark and trundling like a tank. To get a better view, I turned on the flashlight on my phone and used my Canon camera to take photographs and video. I'd never seen anything like it before.
Here is what the light looked like trundling along in the dark. The color seemed to shift from blue-green to yellow and back.
And here is the creature that produced that light:
After consulting the internet, I believe these were firefly larvae. Apparently the larvae of all fireflies glow just like the adults, and they are often called “glow worms” in America. The light they make seems to be for a different purpose than the light of adults. In larvae, it seems to be – as with the pleasing fungus beetle – yet another warning signal that the insect is both poisonous and disgusting. In adults, the light seems to be used by males and females to identify mates of the appropriate species, and by females to pick out the choicest mates.
Does anyone know what species these little guys belong to?
It was a magical natural history moment that happened to coincide with a magical astronomical moment. I've been particularly lucky in this regard lately, but as Pasteur said, chance favors the prepared mind – or the eyes of those who place themselves in nature on a regular basis. Still, if it hadn't been for the eclipse, I probably wouldn't have seen them. The light of the fully recovered full moon drowned out the weak lights of the larvae. The Earth eclipsed the Moon, but brought out the larval stars.