Light Pollution and the Insect Apocalypse

This amazing image was taken by Mike Fuller

The next time you finish a meal at your favorite restaurant, instead of complimenting the chef, thank an insect.  They contributed as much to the creation of your meal as the person running the kitchen.   The alfalfa and clover eaten by the grass-fed beef on your plate were pollinated by leafcutter and honey bees.[1]  For your macadamia nuts, mangoes and sesame seeds, thank some bees, beetles, and wasps. Apples. apricots, and avocados are all likewise pollinated by bees, although with the latter, flies and bats also lend a hand.   Pears, peppermint, and pumpkin all get their culinary goodness from bees and flies, as do raspberries, blackberries, peaches, and papaya.  Like to start your day with a steaming cup of coffee or tea? Again, thank the humble bee.  And don’t forget the spice rack and herb garden.  They wouldn’t be the same without insects. Chilies, cardamom, and coriander are all pollinated by insects. Cinnamon trees rely on the Asian cousins of the western honeybee, while insects such as thrips, beetles and flies are responsible for our supplies of nutmeg. The sweet spicy flavor of clove is delivered by flies, bees, and butterflies.  Thyme, rosemary, sage, chives and mint are all pollinated by insects.  Without these warm comforting flavors, your Thanksgiving meal would never be the same.  Even that Thanksgiving staple, the cranberry, is pollinated by bees.  The culinary treats brought to us by insects continue into dessert.  Hungry for something chocolate? You’ll need the services of the chocolate midge, a tiny fly that is the sole pollinator of the cacao plant.[2]  Lose this fly and you’ll never see another chocolate bar again.  In fact, without insects our culinary lives would barely be worth living.

Insects not only help create food; they are food. Together, the estimated 5.5 million species form the biological foundation for all terrestrial ecosystems.  They are the primary food source for many amphibians, reptiles, birds, and mammals. Even hungry humans turn to insects for nutrition.  Over 3,000 ethnic groups eat 2,086 species of insects across 130 countries.  

The world of food is only one area where we need our six-legged allies.  Insects are responsible for the pollination of about 80% of all trees and bushes.  A few of the more common species that rely on insects for pollination include Cherry, Hawthorne, Buckthorn, Lime, Dogwood, Locust, and many species of Maple.  Insects also play a crucial role in the dispersal of fruit and seeds, with more than 150 species of plants relying on insects for this job.[3]

Insects are also involved in decomposition of animal and plant matter, which is essential for releasing nutrients back into the environment and maintaining the richness and vitality of soil.  Without insects the world would be awash in rotting plants, feces and corpses.[4] 

Dung Beetles use the glow of the Milky Way to help them navigate.

Source: Dung Beetle - Wikipedia Commons Background - Frank Turina

If we had to pay all the insects for their contribution to society, the cost would be astronomical.  Ecologists John Losey and Mace Vaughan, estimated the economic contribution of insects in the United States alone at more than $57 billion, and that figure does not include their role as pollinators.[5]

In the 1960s and 1970s, along country roads that led to grandparents, aunts, uncles, and cousins, scenes of horrific carnage played out on the windshield of our old Chevy Impala.  During the 90-minute drive on those warm summer evenings, hundreds if not thousands of insects of all shapes and sizes met their end on that curved piece of glass.  It wasn’t uncommon to have to pull into a gas station and scrub evidence of the slaughter off the car.    But these days the trips along those western Pennsylvania roads are a lot less gruesome, as populations of many insect species have been steadily declining.  In 1996, Anders Pape Møller, a biologist living in Denmark, began an innovated research project that capitalized on the killing prowess of your average car windshield.  Møller got in his Ford Anglia and drove down country roads in rural portions of northern Denmark.  At the end of each trip, he counted the number of dead insects on his windshield.  He did this again and again and again for twenty years, from 1997 to 2017.[6]  The data that Møller collected showed a striking trend. The abundance of flying insects decreased by more than 80%.[7]  Møller’s research confirmed what a number of other studies had shown: insect populations are declining at an alarming rate[8]

There are multiple factors behind declining insect populations. Loss and fragmentation of habitat; invasive species; contamination by pesticides and other chemicals; the spread of pathogens and parasites; and climate change are just a few of the stressors that insects face.[9]  These factors often interact and compound, resulting in huge reductions in numbers.  In recent years, another often overlooked stressor has been identified as a driver of insect declines: light pollution. 

With light pollution increasing at rates approaching 2 percent per year, naturally dark environments are getting harder to find.  According to the New World Atlas of Artificial Night Sky Brightness, over 23% of the land surface of the planet experiences night skies that are brighter than they should be[10], and in the last 30 years levels of light pollution have doubled in prime insect habitats [11]. A recent article examining 229 studies documenting the effects of light pollution on insects posited that “artificial light at night – in combination with habitat loss, chemical pollution, invasive species, and climate change – is driving insect declines.” The authors concluded “that artificial light at night is another important – but often overlooked – bringer of the insect apocalypse.” The article demonstrated the myriad ways in which artificial light impacts insects including changes to foraging patterns, reproduction, predation risk, and development of offspring.  According to Brett Seymore, a coauthor of the article, human-caused lighting “can affect insects in pretty much every imaginable part of their lives."[12]  For instance, mayflies are often confused by light bouncing off asphalt and lay their eggs in the street instead of a lake or stream. This is a particular problem in areas where roadways and other structures cross or are adjacent to bodies of water.  When light bounces off of roads and other smooth, dark surfaces it becomes polarized. In natural environments, light is most commonly polarized when it reflects off of water. However, smooth surfaces like roadways can trick insects into thinking they are landing on the surface of a lake or stream.   Asphalt can polarize light more effectively than water, so to a mayfly looking for a good place to lay her eggs, roadways can look more like water than actual water.[13]

Mayflies laying eggs on surface of lamp-lit bridge over the Danube River in northern Hungary

Source: Szaz, D., et.al. (2015). Lamp-Lit Bridges as Dual Light-Traps for the Night-Swarming Mayfly, Ephoron virgo: Interaction of Polarized and Unpolarized Light Pollution. PLOS ONE, 10(3), e0121194.

We witness another impact every time we sit outside on a summer night watching clouds of moths and other insects swarm under our porchlights.  It’s estimated about one third of those bugs swirling around our lights die by morning.  They either become snacks for hungry predators or simply die from exhaustion from endlessly circling the glow.[14]  A study conducted in the U.K. attempted to quantify this effect and found that moths exposed to street lights produced half as many caterpillars as those living in similar areas without lights.  Modern LED streetlights appeared to have the biggest impact.[15]

As expected, the decline in insect populations is rippling through the food chain.  Bird populations are in decline around the world and species that feed on insects are faring far worse than those that find nutrition from other sources.[16]  Møller found that local populations of Barn Swallows and other birds that feed on insects declined as the number of insects dwindled.[17] The ripple effects are starting to become apparent in human communities as well.  There is evidence that harvests of blueberries, apples, cherries, and other crops are being affected by a lack of bees, and farmers in China have resorted to pollinating orchards by hand – a tedious and labor-intensive practice.[18]

Fortunately, this is a problem that we can easily solve. It is not costly or technically challenging.  It only requires a basic understanding of the problem and a willingness to act.  If a light is not needed, if it doesn’t have a clear purpose, don’t install it.  If it already exists, remove it.  Use the minimum amount of light necessary and shield fixtures to prevent stray light from spilling into natural areas and other insect habitats. Install timers and motion sensors to help ensure that lights are only on when they are needed and use amber lights that are less likely to attract insects.[19]  By following these simple steps to reduce light pollution we can help alleviate a major stressor on insect populations. 

So, all of you chocolate lovers and self-described foodies help spread the word.  If you want to continue to enjoy your decadent desserts and five-star meals, you need to get on board and reduce your lighting footprint.  And remember, the next time you leave your neighborhood restaurant with a belly full of your favorite food, thank an insect.

Endnotes

[1] Pollinated Foods. (n.d.). Pollinator.Org. Retrieved April 24, 2022, from https://www.pollinator.org/pollinated-food

[2] Milman, O. (2022). The Insect Crisis: The Fall of the Tiny Empires That Run the World. W. W. Norton & Company.

[3] WSL (EN), S. F. R. I. W.-. (n.d.). Insects in the forest ecosystem. Retrieved April 24, 2022, from https://www.waldwissen.net/en/forest-ecology/forest-fauna/insects-invertebrates/insects-in-the-forest-ecosystem

[4] Milman (2022)

[5] Losey, J. E., & Vaughan, M. (2006). The Economic Value of Ecological Services Provided by Insects. BioScience, 56(4), 311–323. https://doi.org/10.1641/0006-3568(2006)56[311:TEVOES]2.0.CO;2

[6] Milman (2022)

[7] Møller, A. P. (2019). Parallel declines in abundance of insects and insectivorous birds in Denmark over 22 years. Ecology and Evolution, 9(11), 6581–6587. https://doi.org/10.1002/ece3.5236

[8] Hallmann, C. A., et.al.  (2017). More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLOS ONE, 12(10), e0185809. https://doi.org/10.1371/journal.pone.0185809;

Fox, R., et.al. (2014). Long-term changes to the frequency of occurrence of British moths are consistent with opposing and synergistic effects of climate and land-use changes. Journal of Applied Ecology, 51, 949–957. https://doi.org/10.1111/1365-2664.12256;

Vogel, G. (2017). Where have all the insects gone? Science, 356, 576–579..

[9] Owens, A. C. S, et.al. (2020). Light pollution is a driver of insect declines. Biological Conservation, 241, 108259. https://doi.org/10.1016/j.biocon.2019.108259

[10] Falchi, F., et.al. (2016). The new world atlas of artificial night sky brightness. Sci. Adv. 2, e1600377.

[11] Koen, E.L., et.a. (2018). Emerging threat of the 21st century lightscape to global biodiversity. Glob. Chang. Biol. 24, 2315–2324 ;

 Kyba et al. (2017). Artificially lit surface of Earth at night increasing in radiance and extent. Sci. Adv. 3, e1701528.

[12] Owens, et.al. (2020)

[13] Brahic. C. (2009). Wildlife confused by polarised light pollution. New Scientist. Retrieved April 25, 2022, from https://www.newscientist.com/article/dn16380-wildlife-confused-by-polarised-light-pollution/

[14] Daley (2019)

[15] Boyes, D. H., et.al. (2021). Street lighting has detrimental impacts on local insect populations. Science Advances, 7(35), eabi8322. https://doi.org/10.1126/sciadv.abi8322

[16] Milman (2022)

[17] Moller (2019)

[18] Milman (2022)

[19] Five Principles for Responsible Outdoor Lighting. (n.d.). International Dark-Sky Association. Retrieved April 24, 2022, from https://www.darksky.org/our-work/lighting/lighting-principles/