The effects of light pollution on night pollinators
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Anne-Marie Walker
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Not long ago, one could gaze at the night sky and see the Milky Way. Light pollution, or artificial light at night, now significantly impedes our view of the Milky Way; air pollution contributes, too. Light pollution is growing at an ever faster pace, driven in part by the transition from incandescent lighting to LED, which, while reducing the cost of lighting, has increased the incidence of night lighting. Scientists report the impact of light pollution on animals, plants, and pollinators is defined by how it alters the behavior of animals, plants, insects, and humans. In the case of humans, artificial light interrupts the circadian rhythm, the sleep-wake cycle. In the case of plants, light, a key energy source for photosynthesis, also regulates developmental processes. Interrupting day-night patterns has consequences. Trees illuminated by streetlights bloom and leaf out sooner and keep their leaves longer in fall. Artificial night light may prohibit some cacti species from flowering and reduce flowering in other plant species. Again, these are the direct effects of interrupted day-night patterns.
Night-pollinating moths are attracted to apple blossoms, pollinating as much as bees do in the day. Photo: Anne-Marie WalkerLight pollution also adversely impacts the behavior of insects and animals. One-third of all vertebrates and almost 2/3 of invertebrates are nocturnal and active at night. To navigate at night, insects use the stars and the moon. Light pollution disturbs natural navigation; visualize the moth attracted to the porch light. Moths are the largest group of night pollinators. Distracting moths from feeding, mating and distributing pollen to pollinate plants is cause for serious concern as it is estimated that moths pollinate 80% of the world’s flora. Many birds migrate at night, and lights confuse them, resulting in fatal collisions. Bats, another night pollinator, emerge around sunset to feed on mosquitoes and other pesky insects while pollinating flowers and fruits, including figs, dates, guava, mango, and agave. Light pollution causes bats to delay feeding, exposes them to predators, and causes them to abandon roosts where their young await their return. Scientists are beginning to calculate the value bats provide agriculture as they eat up those insects; perhaps as much as $50 billion that would otherwise have been spent on pesticides to control insect pests.
Plants and pollinators have co-evolved. A 2019 study traced the tight co-evolution of flowering plants and moths and the importance of pollen transport by moths who travel longer distances than bees that forage near specific nest locations. Flower type, shape, color, odor, nectar, and structure predict which pollinator visits which flower. For example, flowers that attract moths are usually pale in color, sweetly scented, especially at night, and have ample nectar and some pollen. To date, research and information on night pollinators have been limited, but increasingly, researchers are finding that moths contribute significantly to pollination, especially of apples, blueberries, blackberries, raspberries, and peaches. Pollination by non-bee pollinators like flies, beetles, moths, butterflies, wasps, ants, birds, and bats equals pollination provided by bees. Moths visit many other flowers, including yucca, morning glory, honeysuckle, cherries, plums, azaleas, and rhododendrons. Plant larval food like viburnum and blueberries to attract moths to your garden. Also, plant a diversity of flowers, including those with long, tubular flowers like penstemon, nepeta, and California fuchsia.
Pacific Dogwood, on Hallberg Butterfly Gardens’ list of Plants for Moon Gardens, attracts Polyphemus moths. Photo: Anne-Marie WalkerDon’t forget to leave some leaves on the ground for winter habitat and remember to turn off the lights lest night pollinators become trapped by light beams and waste time that would otherwise be spent pollinating. Without pollinators, Earth’s ecosystems will not survive. Go to www.marinmg.org for more information on why pollination matters. To reduce artificial light at night, Ruskin Hartley, Director of Dark Sky International, offers these tips: keep light indoors, close shades at night, use outdoor lights only when needed, and shield light from drifting skyward. Restoring our dark skies is a big step to restoring balance to our natural world.
