Light pollution disrupts the natural cycles of nocturnal wildlife by threatening the integrity of the night sky.

Barn with outdoor security light on at night, which is contributing to light pollution

Since the beginning of time, the world has experienced natural patterns of lightness and darkness. This natural rhythm of day and night has allowed the world’s flora and fauna to acclimate to natural fluctuations of light throughout the day and over seasons of the year. Many creatures evolved to use the predictability of lightness and darkness for reproduction, feeding, rest, and protection from predation. Then came humans and light pollution.

Human ingenuity allowed for the creation of artificial light. For modern civilization, the discovery of electricity and our ability to harness this phenomenon to generate light, removed our reliance on the sun as a light source. But while artificial light has brought incredible benefits for humans, it has also caused many problems for the natural world.

Light pollution – defined as extraneous light in the night sky – affects more than 80% of the world’s population. In the U.S. and Europe, 99% of people live under light polluted skies. Light pollution has prevented most people from seeing the Milky Way with the naked eye.

Fireflies lighting up in nighttime field
Aerial view of Seattle at night showing light pollution
Grass moth on leaf

How Does Light Pollution Affect Insects?

In addition to obscuring astronomical observations, scientists believe light pollution is one of the leading causes of insect decline. Light pollution disrupts natural processes in nocturnal insects like fireflies and moths. It also increases predation of aquatic insects that lie in wait until the cover of darkness to move or eat.

Fireflies

Urbanization, agricultural intensification, and development have caused habitat fragmentation and destruction that have played parts in firefly decline. But light pollution is also a leading cause of population loss. Fireflies use bioluminescence – light produced by a chemical reaction in a living organism – to communicate and attract mates. Light polluted environments make it difficult for female fireflies to differentiate between male fireflies and artificial lights.

Moths

Moths use transverse orientation ­– the practice of keeping a fixed angle on a distant source of light – to orient and fly in a straight line. When artificial sources of light are introduced into an environment, moths begin to orient by fixating on these lights, which are much closer than the light of the distant moon. When moths fixate on close light sources like street lamps and porch lights to navigate, they are forced to reorient constantly, causing erratic flight patterns.

Aquatic Insects

The nighttime glow of artificial light also affects aquatic insects. Many insects spend their immature life stages in the water. Aquatic insects include mayflies, damselflies, dragonflies, caddisflies, and stoneflies. These larval insects remain attached to stream substrate during the day to avoid being eaten by fish. Under the darkness of night, aquatic insects will detach themselves from the substrate and float downstream with the stream current before attaching themselves to new substrate. This practice, called drifting, provides a safe way for aquatic insects to travel since fish cannot see the insects floating above them in the darkness. Artificial light from above, however, creates dangerous silhouettes making it easier for fish to find – and eat – drifting insects.

What you can do:

  • Turn off unnecessary outdoor lights at night
  • Enable dimmers, timers, and motion detectors for lights to save energy and reduce extraneous light
  • Draw curtains and blinds at night so your indoor light doesn’t become outdoor light
  • Where outdoor nighttime lights are needed, use appropriate light shields to minimize light trespass and glare
  • Reduce illuminance by using LED bulbs
  • Avoid blue light in outdoor lighting fixtures

Want to know more? Visit this helpful step-by-step guide for reducing light pollution in the home environment from the International Dark-Sky Association.

Additional Reading and Resources

International Dark-Sky Association (website)

Light Pollution is a Driver of Insect Declines (journal article)

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