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Like a moth to a flame...but WHY?

Those poor moths and other insects - knocking themselves about, circling around that light on our porch or our campfire; why do they do it?

We’ve known and recorded that they do this, back to the time of the Roman empire. Early theories for why proposed that the insects confuse the compact center of light as being the Moon, or that the heat attracts them.

Sam Fabian from Imperial College London, Yash Sondhi from the University of Florida Gainesville, and three colleagues took a detailed look at the paths or trajectories traced by African moon moths flying around an ultraviolet light. They imaged the moths’ motion in high-speed videos at up to 500 frames per second using infrared light, not sensed by the moths, so, not affecting their flight. The moths rarely fly toward the light. Rather, their instinct is to keep their backs to the light, a behavior termed the dorsal-light response. This normally keeps them aligned with the horizon, as they’d need in overall level flight. In the artificial lighting they fly near the light, get confused, and flip over. This generates a path that circles around the light.

Not all insects follow this path that does them no good. Oleander hawk moths don’t respond to ultraviolet light, nor do vinegar flies, so that the research team’s methods won’t work for them. Why some insects respond and others don’t is a next question to study.

This has been an outreach activity of the Las Cruces Academy, viewable at GreatSchools.org

Ref.: Physics Today, 6 Feb. 2024


Vince grew up in the Chicago suburb of Berwyn. He has enjoyed a long career in science, starting in chemistry and physics and moving through plant physiology, ecology, remote sensing, and agronomy.
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  • KRWG explores the world of science every week with Vince Gutschick, Chair of the Board, Las Cruces Academy lascrucesacademy.org and New Mexico State University Professor Emeritus, Biology.