Has Light Pollution Wiped Out the Arthropods?

Is it possible that the vast and consistent decline in the numbers of insects and other arthropods is due to our ever-increasing use of artificial, electric lights at night?

If so, then we are in really big trouble — but we can solve it, by turning out the lights!

Apparently I’m not the only person worried about this idea, which came to me when I thought about the enormous quantities of bugs I used to see 50 or 60 years ago every clear night, flying en masse to their deaths around every electric light bulb they could find. These days, my home’s outdoor lights (when on) seem to catch many, many fewer insects per hour than they did when we moved in 35 years ago… Surely those enormous numbers of dead insects around the outdoor lights must take a toll, and since artificial outdoor lighting is increasing world-wide at a rate of 2 to 6 percent per year, the effect is likely to have gotten more and more severe as time goes on.

Here are a couple of articles on the topic. This one you have to pay to read, unfortunately. This one cites the previous one, but gives a bit more information. Scientists at the University of Virginia are doing a long-term study on the effects of lighting on fireflies (aka lightning bugs): for one species, the females stopped responding to the light signals put out by the males if there was too much light; so if there are fewer female beetles answering, then there will be fewer eggs and smaller future generations. This web page goes into more details. I quote:

“There is an utterly magical time that occurs at tropical dusk. It is when the calls of birds wheeling overhead recede into the distance, and the constant pulse of insect and frog calls fills the air. The inflection point where both sounds are equal in volume coincides with a time when the failing light is ethereal. This heralds the other half of biodiversity, the nocturnal. Within the forest the phosphorescent light of Pyrhophorus beetles leaves green trails in their wake to tempt would be mates to follow. The eerie glow of bioluminescent fungi astonishes, but vanishes instantly in the light of a headlamp. The pale moonlight gives reflected glimpse of bats trolling the surface of oxbow lakes. Overhead one can gaze into black velvet sky to see stars, and comets and the cosmos beyond. This is the stuff dreams are made of.

Other forms of light are less benign to the magic of the forest. The first lights that send their electrical call in wild places draw myriads of insects. A riot of color, form and diversity that is impossible to imagine in advance. But the insects attracted to the electrical beacons will dwindle over time. Every week there will be fewer and fewer. This is because a great many die at dawn. Birds, toads and mammals quickly learn that there is a ready meal at the lights every morning, and that there is nowhere for the transfixed nocturnal denizens to hide. Ants too are regulars at the lights. With organized effectiveness they incessantly carry away the disoriented, the wounded and the dead. There are further consequences of artificial light as well.

Even the most urbanized person cannot fail to pause at the sight of butterflies. Butterflies are insects that require light of the sun to fly, to reproduce, and to flourish. Daylight is their realm. Nonetheless, a major part of their life cycle, the caterpillar, is a creature often active only at night. To find many caterpillars one must be armed with a flashlight and use the cover of night. The introduction of artificial lights in natural areas has a generous impact on the diversity, distribution and the abundance of butterflies. With electric lights come the roads. With roads come vehicles, people, habitat destruction and more lights. This is quickly attended by a reduction in the species of both adult butterflies and the food plants their caterpillars depend on for survival. The area becomes the realm of common weeds, and this reduces butterfly diversity even more. Fewer plant species equates with fewer butterfly species. This is not illusion or fancy, but common sense that even a child can grasp and measure its truth.

I never thought that so many places dreamed of in my youth could be marked so deeply by the human hand. Crucial details embodied in the concept of forest held by our predecessors are lost by each passing human generation. I understand that during my grandparent’s lifetime large carnivores, herds of elephants, and vast expanses of tropical wilderness were common. My experience has been less rich. Many times I’ve tried to imagine the tropical forests experienced by naturalists a century ago and concluded that they would be shocked at the current scale of decimation, and the intruding pervasiveness of electrical light. In their eyes, our concept of forest would lack depth and vitality. Where is the tropical wilderness? When its absence is finally recognized will we try to reconstruct it like historians who earnestly, but vainly attempt to recreate the vital spark of a culture that has passed from living memory? How will we account for and connect all the parts?

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3 CommentsLeave a comment

  1. Maybe it is because of LED lights.

    “An LED bulb with a CCT below 3600K will emit warm or ultra warm white light that’s not easily seen by bugs.”

    https://www.superbrightleds.com/blog/led-lights-attract-bugs/1697/

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    • I don’t think it’s just the LED lights – it’s all outdoor lighting. The brighter it is, and the ‘whiter’ (actually, bluer) it is, the more insects are trapped. Low Pressure Sodium lights emit almost entirely a yellow spectral line, and I don’t think it’s attractive to insects.

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      • I wonder what global warming’s impact will be on insect life.

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