Why can’t insects resist the allure of lights at night?

Why there’s always a cloud of insects buzzing around your outside lights at night has remained a bit of a mystery since the Romans noticed they could use lights to trap insects, but now international scientists have shed some light on the reason. They say artificial lights make it hard for flying insects to orient themselves to the horizon, after using high-speed infrared cameras to track insects’ flight in 3D, both in the wild and in the lab. They found insects correct their course so their backs are facing towards a light source. When that light source is the sun, this allows them to hold a steady flight path oriented to the horizon. But artificial light means they’re constantly and erratically correcting their flight path, causing vertigo and making it appear that artificial lights are attracting them. The authors say we can improve the lives of insects by keeping artificial outdoor light at night to a minimum.

Journal/conference: Nature Communications

Link to research (DOI): 10.1038/s41467-024-44785-3

Organisation/s: Imperial College London, UK, Florida International University, USA

Funder: Financial support was provided by the European Research
Council (ERC-StG no.804315 ‘Vision-In-Flight’ to HTL), National Science
Foundation (NSF IOS-1750833 to JCT), and U.S. Air Force Office of Scientific
Research (AFOSR MURI award FA9550-22-1-0315 to JCT). Additionally,
YS received support from a DYF award from the FIU Graduate
School. Fieldwork was supported by the following: a Tropical Conservation
Grant from the Susan Levine Foundation, a National Geographic
Explorer Grant (EC-82941R-21 to YS & STF), a Lewis Clark
Exploration Grant from the American Philosophical Society, and a Tinker
Field Research Collaborative Grant.

Media release

From: Springer Nature

Investigating why flying insects gather at artificial light

Artificial light may impair insects’ ability to correctly orient themselves to the horizon, suggests research published in Nature Communications. The findings may help us to understand why flying insects gather around artificial lights.

Artificial light has been known to attract flying insects for many years, with written records from the Roman Empire describing the use of light to trap insects. However, the reason behind the phenomenon is still unclear. Previous research has proposed that insects may be interpreting artificial light as an escape route, or that insects are blinded by the light source, in addition to numerous other theories.

Samuel Fabian, Yash Sondhi and colleagues used high speed infrared cameras to track insects’ three-dimensional flight, both in their natural environment and in laboratory conditions. They examined a range of insects — including moths, dragonflies, fruit flies, and hawkmoths — under a range of light conditions, including point and diffuse UV light sources. They found that insects present a “dorsal light response”, correcting their flight course so that their back is facing towards the light source. With natural light sources such as the sun, this response causes the insect to hold a steady flight path correctly oriented with their horizon. However, artificial light causes erratic and continual correction of the flight path, causing insect vertigo and producing what we see as an attraction to artificial light, the authors suggest.

The authors conclude that further work examining the long-distance impacts of artificial light is necessary, and that we can improve insect habitats by reducing unnecessary artificial lighting at night.


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