Why Are Moths Attracted To Light?

Is there any science behind it?

I expected there to be a straightforward, single answer to this inquiry. But no, this seems to be a mystery. Nocturnally active moths are usually attracted to light sources as you have noticed. This event is known as positive phototaxis.

Ultraviolet (UV)[1] lamps, invented for medical purposes, greatly increased moth attraction. Philip Callaghan developed the infrared theory of light attraction. He said that the UV light pumped moth female pheromone molecules in the air into an excited state, so they emitted photons of infrared microwave radiation that could potentially be detected by sensilla on the male antennae, which he postulated were the right size to function as waveguides.

Male moths are more mobile and this theory does not explain the female’s attraction to light. An experiment in 1978 by Robin Baker and colleagues at Manchester University said that the range of light attraction for moths is just a few feet. German trials show that street lights may attract moths from 30-80 feet away. The attraction seems to be for the moths that just happen to fly near enough.

Moths are attracted to moonlight and some say this makes them fly higher on bright moonlit nights. Lack of competition (more lights) will increase the attraction. I’ve been fishing at night with lanterns that certainly prove this point. The darker the night, the more moths will be attracted to the single light source. Tropical biologist Daniel H. Janzen[2] has noticed that some moths can turn off their phototactic response at times. This happens when maybe a food source, like nearby flowers, could be a better attraction than the light.

Some moths tend to migrate and the night sky may give them navigational directions. Using the lighter night sky, against the darkness below, to guide them could possibly explain their disorientation due to artificial light. There is no evidence they have an internal geomagnetic compass system to guide them. A white light will attract more moths than yellow light. Yellow is a wavelength moths don’t respond to.

I remember that my grandparents always had yellow lights on their porches. I’ve also noticed that once near the light source they don’t just go “oh just a light bulb” and immediately fly away. There are theories that flying away will render them blind, just like when you look into a bright light, and they are afraid to flee into the unknown.

Could it be the heat? The darkness cools the air and they could be attracted to the light as a heat source eb=ven though it is often deadly. Like how your cat is attracted to the hood of your car when you get home.

It is a moth mystery as some spiral inwards, others head straight on but then orbit. The time of night and the moth’s gender also makes a difference. Why are moths attracted to light, no matter what kind it is? They will pretty much remain dormant in the dark, moths don’t actually like to fly in no light whatsoever.



Footnotes
  1. Ultraviolet (UV) is a form of electromagnetic radiation with a wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights. Although long-wavelength ultraviolet is not considered ionizing radiation because its photons lack the energy to ionize atoms, it can cause chemical reactions and causes many substances to glow or fluoresce. Consequently, the chemical and biological effects of UV are greater than simple heating effects, and many practical applications of UV radiation derive from its interactions with organic molecules.
  2. Daniel Hunt Janzen (born January 18, 1939, in Milwaukee, Wisconsin) is an American evolutionary ecologist and conservationist. He divides his time between his professorship in biology at the University of Pennsylvania, where he is the DiMaura Professor of Conservation Biology, and his research and fieldwork in Costa Rica. Janzen and his wife Winifred Hallwachs have cataloged the biodiversity of Costa Rica. Through a DNA barcoding initiative with geneticist Paul Hebert, they have registered over 500,000 specimens representing more than 45,000 species, which has led to the identification of cryptic species of near-identical appearance that differ in terms of genetics and ecological niche.



Sources

Moths: A Complete Guide To Biology And Behavior by David Lees and Alberto Zilli
How Stuff Works
Trappify
All Things Pest Removal


Author: Doyle

I was born in Atlanta, moved to Alpharetta at 4, lived there for 53 years and moved to Decatur in 2016. I've worked at such places as Richway, North Fulton Medical Center, Management Science America (Computer Tech/Project Manager) and Stacy's Compounding Pharmacy (Pharmacy Tech).

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