Nocturnal adaptations of moths
Moths make up the third most diverse insect group in New Zealand, and their day/night habits are also diverse. While most moths are nocturnal (active at night), others are diurnal (active during the day) or crepuscular (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.
Orocrambus fugitivellus, a diurnal moth endemic to New Zealand
Orocrambus fugitivellus has only been found in a small area of the plains of the Mackenzie Basin. The males fly by day. The female has very small wings and is completely flightless but also active during the day. This moth is a threatened species.
Nocturnal navigation
Nocturnal moths first evolved 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 geomagnetic signals – the Earth’s magnetic field.
Collecting moths
Dr Robert Hoare, of Manaaki Whenua – Landcare Research, takes us on a moth-collecting expedition. Join Dr Hoare as he goes out at night to collect moths for scientific study.
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 dioxide (CO2) at night. Moths can detect these CO2 emissions and use them to find the flowers.
Moth movement around a light source
Moth flight is altered by nearby light sources. In this illustration, a moth is circling around a candle flame. It gets confused and keeps adjusting its flight. By doing that, it circles nearer and nearer to the flame.
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 star 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.)
Heath trap
The Heath trap is a portable light used for collecting moths. As moths fly towards the light, the fins deflect moths into the base, where they settle amongst cardboard.
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 – was 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 ecosystems.
Acknowledgement
Angus Gaffney produced this article while completing a third-year Otago University internship paper with the Science Learning Hub.
