Why Moths are Obsessed with Lamps | National Geographic

The story of the lamp in the moth is one of fatal attraction. The theory is that these primarily nocturnal insects have evolved to travel by the light of the moon and the stars. This way of travel is called transverse orientation. An easy way to think about transverse orientation is to imagine a sailor traveling in the direction of the North Star.

In theory, moths similarly follow the light source at a precise position and a precise angle to their bodies. This is how moths would navigate for millions of years by the light of the moon. What moth evolution couldn't account for was the proliferation of constant electric light in our modern world.

When Thomas Edison patented the light bulb on January 27th, 1880, it was a bad day in moth history. These light bulbs began to act as artificial moons, confusing moths and overwhelming their senses. Since moths are accustomed to orienting to distant light sources, they can be easily disoriented when a closer light source, like a porch lamp, comes into view.

When there are really bright lights or ultraviolet lights, the draw becomes almost irresistible. Insects respond to ultraviolet light far more than any other wavelength at night; an ultraviolet source is a super stimulant to a moth. These artificial moons make moths easy targets for predators like birds, bats, and many other animals.

While much is still to be learned about moth behavior, one thing is certain: the moth's obsession with lamps often proves to be a fatal one. [Music]