I’ve always appreciated the wry humour of Ogden Nash and he managed to capture my sense of natural history quite nicely with:
“The firefly’s flame,
Is something for which science has no name.
I can think of nothing eerier,
than flying around with an unidentified glow on a person’s posterior.”
We’ve got a bumper crop of these garden insects this year and they flicker and flash away at night to produce a fairy landscape in our gardens.
It’s Really About Sex
Well, they might look like fairies but it’s really all about sex. Fireflies are actually flickering away (they flicker in the daytime too but we can’t see it because of the sunlight) to attract a mate. Scientists have just discovered that the chemical switch that turns the light on and off is nitric oxide (NO). Nitric oxide is an important biochemical control agent in many species (including humans) because, in humans at least, it controls the dilation of blood vessels and the transference of signals between brain neurons.
Not to be too delicate about it but its importance in human sexuality has been exploited by modern drugs such as Viagra. So, do we have a bunch of insects in the garden turning on and off by using Viagra? Not exactly.
The Science Behind The Light
Fireflies (who flash in distinct patterns) produce the light in special cells called photocytes located in their stomachs. The photocyte contains two chemicals called luciferin and luciferase (named after the fallen angel Lucifer) that when combined with oxygen and body energy briefly mix together.
The combination of these two products is not stable (like oil and water) and as they separate they produce light. The more oxygen the insect allows into its stomach, the more light is produced.
The firefly is not alone in producing bioluminescence (bio – from life and luminescence – light) in the natural world but it is one of a very few creatures that controls it to such a fine degree.
This also explains a major question I had as a kid – why do these bugs glow like mad if they are killed on the windshield of a moving car. The answer is deceptively simple – as they smash into the windshield, oxygen rushes into the abdomen and the resulting glow is like a fire starting to go out of control. Unfortunately, the insect dies and the glow dies as well.
Three Reasons Fireflies Flicker.
This control is important because not only
- the firefly is trying to attract a mate,
- It is also warning birds not to eat it.
- to broadcast a danger signal
The chemicals used to create the light are quite bitter and predators such as birds and bats are warned off.
The third reason fireflies light up is to broadcast a danger signal. If a firefly is caught in a spider web, it will start to flicker constantly as a warning to others.
Even though there is an 80% chance the beetle will escape, this flickering warns others not to get caught as well.
Sometimes though broadcasting a danger signal can backfire. With over 1900 different species worldwide and over 170 in North America, there has to be a bad guy in the bunch and there is.
Called a “femme fatale” the female of this species eats other fireflies (including her own mate) and if she sees a danger sign, she’ll wander over to see if she can partake of the feast. It has to be said that the femme fatale is not stupid – she starts eating the distressed firefly from the head back and doesn’t touch the bitter tasting abdomen.
This is the reason fireflies flicker when you put them in a jar – they are broadcasting a danger signal. Wouldn’t you broadcast a danger signal if somebody put you in a jar?
With Only Two Weeks To Live
Actually, putting them in a jar is a pretty cruel thing to do because they only have two weeks to spend flittering around lighting up our gardens. That’s as long as they live above ground.
They spent the previous two years underground as larvae, eating worms.
So, two years underground and two weeks as fireflies.
I’ll never put one in a jar again.
How Do They Recognize Each Other?
With over 1900 species worldwide and every continent except Antarctica, you’d wonder how they can recognize each other.
Most use a different sequence or length of flashes to communicate while others use scent (pheromones) to attract a mate. Some of the females are wingless and flash to attract males out of the sky to their location.
Different species also have habitat preferences; some prefer woodland while others are open fields or wetland marsh area dwellers. A few flash mostly at dusk while others don’t start until it is very dark out.
There’s even a color difference – with shades of yellow, green and amber being the colors of choice.
It’s Not Nice To Play This Trick But…
You can play games with this insect if you are patient.
Take a flashlight into the garden and sit quietly until you see a male flying about blinking his lights.
There are two courses of action you can take.
You can repeat his flash sequence and timing back to him to see if he responds (in some species the males and females have the same pattern, in others the pattern is different and you may have just told him you’re a male too).
If he blinks again, you can repeat your blinking and he may very well come right over to visit.
The alternative is once he has blinked – wait and see whether there is a responding blink from ground level that is different. This is the female and you can now either copy the male or female to see what happens and how many fireflies you can fool.