June 8th, 2006
light up the night!
A few weeks ago, I wrote about diurnal fireflies — members of the Family Lampyridae that do not produce flashes of light at night. They’re still around, but they’re now upstaged by the light show produced by their nocturnal kin. For the next few weeks, the yard will be filled with green glows and streaks of light on occasional evenings when weather conditions are just right. Don noticed the first good showing of fireflies last Friday evening (June 2nd), with dozens of fireflies zooming and arcing above the tall meadow grass around our house and barns. But what is a firefly? Who is the insect behind that neon glow?
Contrary to their name, fireflies are actually beetles (Order Coleoptera), and all species belong to the Family Lampyridae. Typical of other beetles, they have elytra (wing covers) that protect wings that are kept folded beneath until the insect is in flight. In the photo on the left (click on it to see a larger view), the elytra have been flipped open and the longer, black wings are visible, as is the segmented abdomen. I took this photo just as the firefly was about to take flight from a leaf.
Fireflies emit a sequence of flashes with a luminous organ in the end of the abdomen. You can see that part of the abdomen in the above photo of fireflies in a plastic container. Males and females of each species have certain flash sequences that help them to locate each other. Flash recognition is important to survival as some some species of fireflies are predatory on others. If you’re interested in knowing more about predation among species, check out this page which explains how female Photuris fireflies can imitate the flash sequence of Photinus females in order to attract males which they will devour. Their goal is to absorb a protective substance known as lucibufagins which helps to repel spiders, birds and other predators. Quite fascinating.
Above is a close-up of a female firefly atop of a milkweed flower. As you can see, she’s quite a curious-looking creature, with a large pronotum that covers the back of her head. When I photographed her, she was standing with her abdomen inside part of a milkweed flower and was rocking back and forth almost as though she might be laying eggs. However, as fireflies are supposed to lay their eggs in damp soil, it seems unlikely that that’s what she was up to. I’ve tried to find out if this is common behaviour, but haven’t yet come across anything in firefly literature. The only other possible explanation I can come up with – and this is a total shot in the dark – is that perhaps the female is able to acquire some repellant substance from the milkweed as they contain cardenolides which is the toxin that protects Monarch butterflies. If anyone reading this happens to have come across this behaviour or knows of a reference pertaining to it, please leave a comment.
Some technical notes for the photo buffs among you: I suspect that there are a few of you who might be curious about how I managed to make the animated .gif of the flashing fireflies. Well… it took a bit of experimentation. I first tried to photograph the fireflies with my still camera, but couldn’t get that to work at all. My next attempt was with my older Canon ZR25 DV-cam set on “low light”. I was able to make reasonable movie clips using it as camcorders really can produce images under near-impossible conditions. My next challenge was to find a way to tape footage of the fireflies flashing. My first experiment was with an aquarium with a screen on top and about a dozen fireflies captured in a jar out in the yard one evening. I thought that they might put on a light show which I could tape. Unfortunately, all they seemed intent upon doing was escaping, which most of them managed to do in record time. The worst of it was that I had set the aquarium up on a table in our bedroom, so we had fireflies zooming around over our bed every time we turned the lights off for about two nights – until I had captured everyone and turned them loose outside. I finallly struck on the idea of putting a few fireflies inside of a plastic cassette container and shooting video footage of the fireflies within. At first they didn’t want to flash, but quite by accident, I found that they would flash like mad if they could see the red indicator light on the side of the DVcam that flashes when the camera is plugged in and charging its batteries from an AC outlet. The sight of the red flashing light may enrage them, or perhaps produce some other reaction. In any case, it worked well and everyone performed admirably as I shot a couple of minutes of footage before releasing them into the meadow. Once I had the footage, I saved several of the best “flashes” as .jpegs and then tossed them all together in a .gif program — probably GifBuilder (can’t remember now as I did this last July). I should have “equalized” the images in PhotoShop first, but didn’t know about doing so at the time, so it’s rather imperfect. However, it accomplished what I really set out to do in the first place — which was to photograph flashing fireflies so that I could share them with a friend who has always wanted to see them. I may do some more experimenting this year, so stay tuned for a possible follow-up.
Tags: fireflies, Lampyridae, Photuris, Photinus