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
June 9th, 2006 at 9:01 am
Cool bug, cool animation, Bev! Thanks for the tips on photography. I’ve tried a few times to photograph fireflies in the field at night. There certainly are a number of problems - your solution is a neat one.
One of my problems was that ours seem to quiet down after dusk, when it gets really good and dark, and I needed that really good and dark for the field approach I was attempting. The other problem is that I was setting the camera up on a tripod with a wide angle view (28mm) and at a distance the flashes just were never bright enough to register much.
June 9th, 2006 at 9:49 am
Brilliant informative post! Have you written any books on insects? Between you and Wayne, my nature education is widening. I have wanted to get some firefly photos but part of my problem is being too tired at night to stay up. I am better at sunrise photos.
June 9th, 2006 at 10:47 am
Most lampyrids are deadly poisonous (see reports of pet lizards dying after being fed a single firefly), but interestingly, they don’t have the garish red or yellow warning coloration that other poisonous animals favor. Instead, they glow! It’s an evolutionary two-for-one, both warning and sexual signalling (and there might be other advantages to it too). Probably the warning function evolved first, since the larvae also glow, even in species that don’t flash as adults. But why such an atypical way to signal their inedibility? Presumably the chemical reaction that produces light bootstrapped on some other reaction that was already present. Just one of those counterintuitive evolutionary stories.
June 9th, 2006 at 12:30 pm
Vasha makes a very interesting point that I hadn’t thought of. From your earlier post on this subject, Bev, we talked about why the kids would bother to have a glow if it were simply for sexual signalling. I hadn’t thought of warning at the time.
Sort of like feathers in birds originally and hypothetically adaptations for heat exchange, and later adapted for flight.
June 9th, 2006 at 12:56 pm
Wayne - Yes, the photography is quite a challenge. The best luck I’ve had in the field is with the DVcam. You can actually walk right up to a flashing insect and shoot footage of it up close and get a pretty good impression of how it actually looks in the dark. I’m sure that some of the more recent models of DVcamcorders would do a really good job of it. By the way, the DVcam footage is quite good compared to the frame grabs in the .gif. The DVcam is also not too bad at capturing the look of several fireflies in flight in the meadow, although you have to be fairly close to them while shooting. I haven’t figured out a way to shoot good images with the Nikon CP8800 at yet, but my next experiment is to try shooting little .mpeg movies with it, then importing them into iMovie to extract some stills. If that works, I’ll post the images.
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O.W. - No, I haven’t written books on insects, but I used to do a lot of writing of agricultural teaching publications. Insects are just a hobby, but one that I do spend quite a bit of energy on - between the photography and learning more about their life cycles.
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Vasha - Yes, it is interesting about the flashing being the main “warning” to potential predators. I suppose that does jive with their nocturnal behaviour though as they seem quite secretive during the day — although I did shoot a photo of one found on a milkweed leaf yesterday. Being night active, their bright flash might be their best defence against predators. As far as sexual signalling, the flashing is also an interesting adaptation for a nocturnal insect. Many nocturnal insects depend on scent or sound rather than sight. In any case, they’re certainly interesting insects!
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Wayne - Yes, it is interesting. I wonder how active the larvae are during daylight as opposed to night. If they move mainly at night, then that would explain the glow as a warning signal. There’s probably some literature on all of this, but I haven’t had time to investigate further — perhaps a project for some rainy day! (-:
June 9th, 2006 at 3:01 pm
Bev, I hadn’t even thought of nocturnal habits driving them to light instead of color signals. Duh! By the way, I’ve been reading this blog daily for months now. I’ve always enjoyed insects but I’m paying more attention to them now, seeing something new almost every day (especially tiny ones of course, just about impossible to identify). Coincidence: I was sitting outside reading when, thwap, a big rectangular shiny-green beetle landed on the page. I practically shouted, “It’s a six-spotted tiger beetle!” I’d never seen it before, but both you and Wayne had posted pictures of this species within the previous week. It was just a surprise to see pictures come to life (I live somewhere in between the two of you, in central New York).
June 9th, 2006 at 3:18 pm
Vasha - it was Thingfish23 that got me going on insects, and Bev who cemented me on looking under every itty bitty leaf for things. And here I am a plant person. I started out on butterflies but now I’m mistaking flies for wasps. How about that for progess!
June 9th, 2006 at 3:38 pm
Vasha - Since I began studying insects, I’ve had to turn my way of thinking almost upside down. Their life cycles are so complex, the dangers so many and varied, and their survival strategies so diverse. There’s always something new to learn - which is probably why I enjoy studying them as much as I do. That’s neat about you being able to ID the tiger beetle. There’s nothing quite like being able to apply new knowledge!
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Wayne - Well, I’ve read through some of your older posts and you’ve been covering insects and *many* other topics very well for quite some time! As for the flies and wasps, those are very tricky flies that can even fool the bees. Think of them as duck decoys - they look like a duck, but they sure don’t taste like one. (-:
May 3rd, 2007 at 12:26 pm
Then why do they stop flashing when handled, asuming that it is a warning?
May 4th, 2007 at 6:47 am
Pierre - I’ve also noticed that they stop flashing when handled, so I’m not sure if the flashes are meant to warn off larger predators such as ourselves. They might be useful for amphibians and reptiles though. I do think the chief purpose of the flashing is to attract mates, but some species also use it as a ruse to attract other species to kill, so in both cases it’s a kind of lure. One thing that I found interesting (I’ve mentioned it above in my photography notes) was that the fireflies flashed like crazy when they saw the red flashing charging light on the side of my DVcamcorder.