I am working on my certification as a Master Gardener with the University of Arizona Master Gardener Program. I was asked to contribute an article for their monthly Roots & Shoots magazine, so I decided to combine my gardening hobby with my love for the night sky. Enjoy!
QUESTION:
I have heard that light pollution can interfere with nighttime pollinators, reducing the ability of plants to get pollinated. Is this true? What constitutes light pollution? How would my Phoenix garden or yard be impacted by light pollution? Is there something I should be doing?
ANSWER:
The quick answer is “Yes!” It is true, and thee are things you can do. But first, let’s make sure we are on the same page.
According to the International Dark Sky Association, light pollution is the use of artificial light at night taht produces glare, light trespass, and sky glow from inefficient and poorly designed lighting. Light trespass is when your exterior lighting shines beyond the boundary of your property. Sky glow is when improper lighting fixtures allow lighting to shine upward, scattering light so that the sky lights up at night.
Light pollution impacts all life. It not only disrupts your normal daily cycles of day and night, but also that of wildlife, including pollinators. In this article, we will focus on the pollinators that may be moving around at night in your Phoenix yard and garden, how excessive light impacts them, and why it matters.
Brett Seymoure et al. of Washington University in St. Louis co-authored a report where scientists reviewed 229 studies to document the ways light alters the environment so that insects cannot carry out their crucial biological functions. In fact, some researchers have coined a term for it: an incest apocolypse. (https://www.smithsonianmag.com/smart-news/light-pollution-contributes-insect-apocalypse-180973642/)
Consider this statement from the study co-authored by Seymoure et al., “We strongly believe artificial light at night– in combination with habitat loss, chemical pollution, invasive species, and climate change– is driving insect declines. We posit here that artificial light at night is another important– but often overlooked– bringer of the insect apocalypse.”
Researchers say that about half of the millions of insects in the world are nocturnal. Light pollution impacts how insects hunt and mate, and makes them more vulnerable to predators.
Moths are of particular interest to those who are concerned about pollination and they are especially drawn to artificial light. It is estimated that about one-third of the bugs that swarm around those lights die by morning, either by being eaten by predators who find an effortless meal or simply from exhaustion.
Ranger Amy Burnett from the Arizona Game & Fish says that the phrase, “Like moths to the flame,” couldn’t be more true. There was one study where a person captured 50,000 moths in one night, and that’s a lot of moths. If the reproductive abilities of that moth species are not super amazing, they may not be able to replace themselves so easily. (https://anchor.fm/night-sky-tourist/episodes/4-Wildlife–Light-Pollution-with-Amy-Burnett-eo6uvg/a-a468g7r)
“These moths are important pollinators, especially in the Sonoran Desert,” said Burnett. “We rely on night pollinators, such as insects, for our night blooming flowers like the saguaro. We don’t have the long-nosed bats in the Phoenix Valley that pollinate the saguaros in southern Arizona. We rely on moths to pollinate saguaros, agaves, yuccas, and other plants that are pollinated at night. So a reduction in the number of moths that are able to pollinate flowers can have a big impact.”
Most moths are active at twilight and are attracted to lights and the fragrance of the blossoms throughout your yard. Sphinx Moths or Hawk Moths (Sphingidae family) are common in the Sonoran Desert during the spring and summer. They spend the evening visiting many night-blooming plant species, including ornamentals.
Yucca blooms release their most concentrated scent at night and they produce the most nectar in the evening hours. So it’s not a surprise that their most important pollinator the Yucca Moth (Prodoxidae family) flies only at night. The relationship between the yucca and this specific moth is important because they cannot survive without each other. The moth’s larvae depend on the seeds of the yucca plant for food, and the yucca plant can only be pollinated by the Yucca Moth.
Seymoure and Burnett both say that reversing light pollution is as easy as flipping a switch and offer the same recommendations:
- Turn off any light that is not needed.
- Use lights with a warmer color temperature.
- Install motion activators on your lights.
- Shield your lights so the bulbs are not exposed.
These recommendations also coincide with recommendations from the International Dark Sky Association for combating light pollution.
Let’s break down each of these recommendations so we can better understand them.
TURN THE LIGHTS OFF
No one is suggesting that there should be no lights at all, but rather that we should use smarter lighting practices. Light only what needs to be lit for safely finding your way around at night. Once you are home for the night, those lights are not needed and can be turned off.
CHOOSE A WARMER COLOR TEMPERATURE
Lighting has a wide color spectrum range from bright bluish-white to warm amber and red. Bright white light has a strong negative impact on the human eye and on nocturnal animals and insects. Choose a light that is warmer in color, preferably below 3,000 Kelvin. (The color spectrum is labeled on the packaging).
USE MOTION ACTIVATORS
Save money on energy, promote safety, and protect the nocturnal animals and insects by only having lights come on automatically when they are needed.
SHIELD YOUR LIGHTS
Not only will your eyes appreciate blocking the glare from a bare bulb, but fully shielded lights will also attract fewer nocturnal pollinators to their death.
Maintaining a healthy garden and landscape requires you to consider multiple factors and inputs, but protecting your nighttime pollinators is as easy as flipping a switch.
