It’s an almost magical aspect of summer nights in New Hampshire: the sight of fireflies glowing in the darkness, hoping to attract mates. Granite Geek David Brooks recently began to worry about the population of fireflies. It seemed to him like there were fewer of them. So like any good journalist, he went to an expert to gain insight on this observation, and he joins me now to talk about what he found. David’s here now. Welcome.
Tell us who you spoke to and what they said.
I started out by calling all the insect people I know in the state. They all told me to talk to Sara Lewis, who is a biology professor at Tufts. And by sheer coincidence, she has just published a popular science book about fireflies called Silent Sparks. I went to her and said, “Hey, it doesn’t seem like I’m seeing many fireflies, and I’ve also seen some news reports of people very concerned about the population of fireflies. So is this like the honeybees? Are the fireflies crashing?” The answer is: we don’t know, because nobody’s gathered good data about firefly populations in the first place. So you can’t really say they’ve gone down to know how many there are.
That said, we’ve had a few conversations about how in wet springs there are more of certain insects—ticks, mosquitos—and less so in dry springs, and it has been a dry spring.
It has been a dry fall, winter, spring, summer! And that’s exactly part of the reason why it’s hard to say, particularly about insect populations, which can grow and shrink quickly from year to year, and you’re absolutely correct. If it’s dry, you’d expect to see fewer of them. I’ve got wet spots in a field next to my house, which is where I usually see them all, and those wet spots aren’t so wet this year, so the fact that I don’t see much of them…maybe that’s just a reflection of a one-year change in the weather rather than long-term population trend.
And the nature of fireflies is such that they can live for two years, but most of that time is spent underground.
That was one of the things I learned from Sara Lewis. They can live up to a couple of years, but almost all of that time is spent as grubs or larva underground. And they come out and turn into these flying beetles—they’re not flies, despite the name. And they fly around and for many species the males generally glow to attract a mate and then they reproduce, lay eggs, and die. So the part of the firefly that you and I think of is a fairly small part of their lifespan.
The small part where they’re looking for love.
They’re looking for lust. Let’s be honest here.
All right. Well, what role does the loss of habitat play here?
The first thing Sara Lewis said to me is that “We don’t have any data, so we don’t know.” The second thing she said was, “But there’s reason to worry.” And a big part of the reason for worry is what you just said, which is loss of habitat. That comes up all the time in almost all wildlife populations, right? It’s that all these little wetland and boggy areas where they kind of like to live, where the grubs like to be—they don’t handle dry weather well at all. So all these places they like to be, we’ve turned them into parking lots. We’ve drained areas. We’ve made the edges of rivers nice and neat. So it would make sense that the populations are being stressed.
There are a couple other things that affect them. One is pesticides. Lewis talks specifically about pesticides. If you want to get grubs in your yard using a grub pesticide, then realize you’re almost certainly killing off the larval form of any fireflies which would be coming out and being nice in the summer, so that’s an issue. Something that’s a little less usual that’s a real problem for them is light pollution, which makes sense when you think about it.
Well let’s dig into that, because as you mention, males use their glowing properties to attract mates, but if you’re flooding an area with human-made light, that might confuse the females, right?
That’s what seems to happen. And Sara Lewis points this out. You’ll see this happening on a full moon. If you go out during a full moon and you’re in a field where you’re seeing fireflies, when the moon rises, you’ll see all the fireflies move into shaded areas, because they’re trying to get away from the light so they can be visible.
First of all, there’s another thing I didn’t realize is that there’s lots of different species of fireflies. There are 120-150 or so in North America, many of them in North America.
And many do not glow at all.
That’s right. This was a surprise to me. There are fireless fireflies.
And they don’t glow at all, and some that only glow as glow worms. And of course, the flying one. So it’s a small set. And different species give off different colors of light, different frequencies, because they don’t want to interfere with each other. So depending on which species is out at any given time, it is which kind of light is going to most affect them, because there’s obviously outdoor lighting with different frequencies.
But as a general rule, if you’ve got your security lights flooding your back yard, fireflies are either not going to show up at all, or if they show up, they’re not going to find mates, and they won’t reproduce, and you won’t have them later. So one of the simple things you can do (if you like fireflies) is keep outdoor lighting down, particularly in the summer. Different species do their mating dances at different times, but you can keep them all down anyway, so you can see the stars.
And if you do catch one in a jar, keep it for a little while, but then let it go, so it can find some love.
Yeah, unlike those of us who, as children, waited until it was glowing and then squished them so you can rub the glowing stuff all over your hand.
Right, kids, don’t try that at home.