Moths make up the third most diverse insect group in New Zealand, and their day/night habits are also diverse. While most moths are nocturnal1 (active at night), others are diurnal2 (active during the day) or crepuscular3 (active at twilight). Each of these lifestyles has its own advantages. Being active at night means less competition for food and being less likely to be detected and eaten, whereas daylight means there is more light to see and more energy from the Sun. Crepuscular animals can get the best of both worlds.
Nocturnal navigation
Nocturnal moths first evolved4 long before humans invented bright lights. They learned to navigate by using distant celestial objects such as the Moon and stars. Moths navigate by positioning themselves and flying on a fixed angle relative to these celestial light sources. If the position of the Moon or stars is not obvious, moths instead use geomagnetic5 signals – the Earth’s magnetic field6.
Why are nocturnal moths attracted to the light?
It is not yet fully understood why moths appear attracted to bright lights, but there are several hypotheses. It could be that certain lights (such as candles) emit specific wavelengths that attract moths – perhaps like a female’s pheromones, which attract male moths. Another possibility is that artificial ultraviolet light is associated with a food source. Many night-blooming flowers reflect ultraviolet light. However, this isn’t necessarily how moths seek out these flowers. These flowers release high levels of carbon dioxide7 (CO2) at night. Moths can detect these CO2 emissions and use them to find the flowers.
The leading idea is that moths use starlight to accurately fly long distances. By maintaining a constant angle towards an object like the Moon or the stars, moths can fly in a straight line. Because the Moon or stars are so far away, the change in the light’s angle is negligible, but when a moth flies toward a close-up artificial light, the angle changes dramatically. Thinking it is a star8 or the Moon, the moth will keep changing its flight angle to keep going in a straight line (keeping a constant frame of reference). The changes mean the moth continually turns towards the light, causing it to spiral and circle around the light source instead. (Heath moth traps take advantage of this downward spiralling behaviour.)
Related content
This article contains more information about the differences between moths and butterflies.
This introduces all our resources on the Ahi Pepe MothNet project. It has resources in te reo Māori and English.
Useful links
Visit the Ahi Pepe MothNet project website for resources and more, including free, downloadable regional guides, in both te reo Māori and English. Watch the video Moth Net: Shedding Light on the Night for an overview of the project.
New Zealand’s Biological Challenge – one of the National Science Challenges – helped to fund the national Ahi Pepe MothNet project. Find out what they are doing to enhance and restore New Zealand’s ecosystems9.
Acknowledgement
Angus Gaffney produced this article while completing a third-year Otago University internship paper with the Science Learning Hub.
- nocturnal: Active at night.
- diurnal: Literally means daily. The term can refer to a daily cycle or any activity or motion that occurs daily.
- crepuscular: Appearing at or active around twilight.
- evolve: To develop gradually. Changes in successive generations over long periods of time.
- geomagnetic: Of or relating to the Earth’s magnetic field.
- magnetic field: The zone around a magnet in which a magnetic force can be detected.
- carbon dioxide: CO2 is a colourless, odourless, incombustible gas. It is a product of cellular respiration and combustion and is an essential component in photosynthesis.
- star: A self-luminous celestial body consisting of a mass of gas held together by its own gravity.
- ecosystem: An interacting system including the biological, physical, and chemical relationships between a community of organisms and the environment they live in.