Remember the summers when so many insects would splatter on your car’s windshield that you had to scrub them off to get a decent view through the glass? You probably haven’t had to do that nearly as often as you used to. And while you may be happy to avoid that chore, it is an unfortunate sign that insect numbers have declined dramatically in recent decades.
Researchers have found that the total mass of insects in some areas has declined by as much as 80 percent since the 1980s, and that has dramatic implications for wildlife, especially for bats and insect-eating birds like flycatchers, swifts and swallows.
One of those insects that is noticeably absent from many fields and forests these days is the popular firefly. I remember fondly the summer days of running through my neighborhood fields and forests just after dusk trying to catch lightning bugs in a glass jar, then watching the captured insects blink on and off until bedtime. It’s an experience that few of today’s children have had, since fireflies are harder and harder to find in any numbers.
An excellent new book titled “Silent Sparks” by a Tufts University professor sheds light on the natural fireworks display put on by native fireflies. Sara Lewis calls the flickering lights a “spectacular bioluminescent courtship display” in which males emit a specific pattern of illuminated pulses. The males of the most common firefly species in New England, Photinus greeni, produce a distinctive pair of pulses separated by 1.2 seconds, followed by a four second pause before repeating the pulses. If he’s lucky, an interested female will reply with a single prolonged flash that rises in brightness before fading.
“Each time he shines his light, the male pauses for an instant in hopes of spotting a female,” she wrote. “So tonight it’s wink, wink, hover and hope … wink, wink, hover and hope.”
Sadly, that hope is more and more turning to hopelessness. Even in locations where firefly numbers are relatively high, males often struggle to find a mate, since females are often outnumbered by males 20 to 1. In many areas, males may flash for days without getting a response.
Repeated flashing by fireflies can be costly, as the illumination not only signals their location to receptive female fireflies but also to predators seeking to eat them.
The reasons for the disappearance of fireflies – and so many other once-common insects – is unclear. Habitat disturbance is an obvious one. Most firefly species are found around fields, forests and marshes, which in many areas have given way to pavement, houses and shopping centers. Pesticides and other pollutants are likely contributing factors as well.
Surprisingly, light pollution has also been implicated in the decline of fireflies. Since the insects use their flashing lights to communicate, the abundance of man-made lighting from street lights, stores and cars is believed to make it difficult for the insects to signal each other. And those species that synchronize their flashes during courtship get out of sync when a car’s headlights pass by.
So the next time you see the flashing of a firefly in the evening, celebrate the memories these cherished insects provide, and mourn the fact that few in the younger generation will be able to share those memories.