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Why Insects are Drawn to Artificial Lights Like a Moth to a Flame

Why insects come to artificial lights, Luna Moth, light bulb, Moon, Images generated with DALL-E2

The age-old question of why bugs are attracted to fly around artificial lights has never had a sufficiently illuminated answer. For years, entomologists have been constantly asked why insects do it, but there’s never been a definite answer. But now, scientists have what they consider the most plausible explanation, and it may not be what you expect. 

Intuitively, people have thought insects come to lights, mistaking them for the Moon’s light reflected from the Sun. Another idea is that insects come to light because they think they see daylight peeking through leaves in the distance. So maybe they head in that direction to escape the darkness.

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Why Do Insects Come to Artificial Lights?

In a new study, an international team of scientists has used technology to answer why bugs come to artificial lights. Using high-resolution motion capture and stereo-videography, they studied the flight of the insects. These included moths, dragonflies, and butterflies in a laboratory setting and in Costa Rica.

Studying the slowed-down footage, they found that insects aren’t steering directly to the light, but like little pilots, they try to orient themselves in space. 

“A team led by biologists Samuel Fabian at Imperial College London and Yash Sondhi at Florida International University argue that when many insects see a bright light at night, they believe they’ve found the direction of the sky and attempt to orient themselves along an up-and-down axis. That instinct prompts them to roll their backs toward the light, mistakenly in cases when the source of illumination is on the ground or mounted horizontally, causing them to go into endless, banking turns like a tiny airplane or to crash-land,” reports the New York Times.

Thus, the insects don’t find the artificial light itself attractive but are disoriented if they happen to fly past one.

“Our results suggest artificial lights may only trap passing insects rather than attract them directly from farther away,” write Samuel Fabian at Imperial College London and his colleagues in a paper on the bioRxiv preprint server,” reported NewScientist.

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Tiny Disoriented Pilots

Like tiny pilots, the insects attempt to “maintain proper flight attitude and control,” as they normally do flying under the night sky. They keep their backs, the upper surface called the dorsum, to the light. 

Unfortunately, as they try to navigate around artificial lights, this traps them in a hazardous loop where they become highly vulnerable. The scientists called it the dorsal light response, caused by a natural reflex (see video below).

Either they will exhaust themselves circling the light or become a meal for a predator, such as a clever spider who figured out how to catch an easy meal. It’s a little sad to think of what they must experience as they try to get back on the right flight path. It’s reminiscent of a whale that beaches itself, confused by sound pollution.

Video by New Scientist about the study of insects and artificial lights:

Light Pollution and the Insect Apocalypse

Scientists know that light pollution is one of the drivers of the worldwide decline in insects, the “Insect Apocalypse.” But it’s just one of many factors.

“As human activities rapidly transform the planet, the global insect population is declining at an unprecedented rate of up to 2% per year. Amid deforestation, pesticide use, artificial light pollution and climate change, these critters are struggling — along with the crops, flowers and other animals that rely on them to survive,” Reuters reports.

Without all insects, humans could be gone in about three months, according to entomologists. In our money-driven world; it may help to consider that insects perform a variety of vital services valued at around $57 billion per year for the US alone. But ultimately, money has no value if there are no insects.

Maybe this is worth repeating:

Money has no value if there are no insects.

There are many simple things individuals can do to help, and one is to simply turn off artificial lights at night and use motion sensors and LED lighting. There are many other easy ways to help:

While some bugs, like bed bugs or mosquitos, are a real pain to people, the vast majority are beneficial and vital to the entire food chain. Dragonflies are one of the insects in the study of artificial lights and are great at destroying mosquitoes and flies. So, here’s more on how to attract dragonflies to your yard.

Video by BilyOh:

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