Historic collections help understand hawkmoth vision
In 2018 Emmanuelle Briolat visited RAMM’s stored collections. Emmanuelle is a researcher at the University of Exeter’s Centre for Ecology & Conservation. In this blog she talks about her interest in hawkmoth vision and how RAMM’s moth collections helped with her research. In a paper published last week Emmanuel and her colleagues explore how artificial lights might affect what nocturnal hawkmoths can see.
Why study light pollution?
Light pollution is a major way in which humans are altering the natural environment. Man-made light sources, such as streetlights change the colour and intensity of lighting in the night sky. The extent of light pollution continues to increase worldwide and the nature of lighting is changing too. We are moving from more orange traditional light sources to energy-saving LEDs, without fully understanding the consequences for wildlife.
At the University of Exeter we are working to better understand the potential impact of artificial lights on nocturnal species such as moths. Evidence is accumulating to show that light pollution can disrupt moths in many ways and at all life stages. We are especially interested in understanding how artificial lighting can interfere with the way moths see the world and the consequences this has for important behaviours such as pollination and communication. We also want to know how they are perceived by potential predators to find out if light pollution might put them at greater risk.
Hawkmoths (Sphingidae) are known to have excellent nocturnal vision. They have three types of cone photoreceptors – cells in the eye sensitive to ultraviolet, blue and green wavelengths of light. They allow the moth to see in colour under starlight.
To see and be seen
Nocturnal hawkmoths are important pollinators. So our first focus was to test how artificial lights might change the way hawkmoths see flowers. To do this we needed objective measurements of the colours of hawkmoth-pollinated flowers. We also measured leaves, grasses and other natural backgrounds. This involves measuring samples with a spectrometer, to quantify which wavelengths of light they reflect.
Hawkmoths have beautiful, intricate and often colourful wing patterns. Wing markings could act as signals to other hawkmoths such as attracting potential mates. Or they can act as visual defences against predators, whether by helping them to disappear into the background like the leaf-like poplar hawkmoth (Laothoe populi), or startling predators with conspicuous eyespots like the eyed hawkmoth (Smerinthus ocellata). So we also wanted to know how light pollution would change the way moths and their predators might see these patterns.
Where RAMM comes in
Testing how a modern problem like light pollution can affect hawkmoth vision may seem quite remote from the collection drawers of museum storerooms. But museum moth specimens provide a great resource for our research. To understand how hawkmoths are seen by other moths and their predators I measured wing colours from specimens at RAMM and Bristol Museum & Art Gallery.
We found all 14 UK nocturnal hawkmoth species in the museums’ collections. Pinned flat in the drawers, museum specimens are ideal for measuring colours with both a camera and a spectrometer probe. Also, having access to museum specimens allowed us to measure specimens without having to find, capture or harm any live animals. More than just convenient, this low-impact data collection was an incredibly important consideration, especially for a project so closely linked to conservation.
Next we combined the measurements of moth and plant colours with measurements of over 20 types of natural and artificial lighting , and information on the visual system of the elephant hawkmoth. As a result we were able to model how hawkmoths would perceive colour contrasts between flowers and vegetation, between different markings on their own wing patterns, and between their wings and natural backgrounds, under a range of potential night-time conditions.
As light pollution can encourage birds to forage later in the evening, or earlier in the morning, we also tested how easy it would be for them to detect hawkmoths hiding on tree trunks or leaves under different lights.
What we learnt and what this means for conservation
Overall, we found that hawkmoth vision was much more vulnerable to disruption by artificial lights than bird vision. Birds couldn’t see colour at very low light levels. Higher levels of any kind of lighting would help them detect moths more easily, so higher light levels could make moths more vulnerable to predation.
However, for hawkmoth vision the kind of light was really important. Some, like mercury vapour lights, replicated natural moonlight conditions well. By contrast, very narrow-band long-wavelength lights, such as orange LEDs or low-pressure sodium lights, essentially blocked all colour vision for hawkmoths.
In between these two categories, some light types had variable effects, depending on light intensity and the specific colours viewed. These included phosphor-converted amber LEDs that are often suggested to be less harmful for wildlife than typical white LEDs. This suggests that we need to be careful when making recommendations for more environmentally-sensitive lighting.
Balancing lighting systems that reduce insect attraction (moths are famously attracted to lights) while still supporting nocturnal vision for the species that rely on it will be difficult. Hopefully the modelling tools we developed can be used to better understand how lighting affects the visual ecology of hawkmoths and other species, to help inform future decisions. By helping to predict how wild moths will respond to future light regimes, museum specimens can play an important role, not just reminding us of the wildlife of the past, but also contributing to conservation efforts in the future.
The full paper is open access and can be read free of charge:
Briolat, E.S., Gaston, K.J., Bennie, J. et al. Artificial nighttime lighting impacts visual ecology links between flowers, pollinators and predators. Nat Commun 12, 4163 (2021). https://doi.org/10.1038/s41467-021-24394-0
- Boyes, D. et al. Is light pollution driving moth population declines? A review of causal mechanisms across the life cycle. Insect Conservation and Diversity 14, 167-187 (2020).
- Briolat, E.S. et al. Artificial nighttime lighting impacts visual ecology links between flowers, pollinators and predators. Nature Communications 12, 4163 (2021).
- Johnsen, S. et al. Crepuscular and nocturnal illumination and its effects on color perception by the nocturnal hawkmoth Deilephila elpenor. Journal of Experimanetal Biology 209, 789–800 (2006).
- Kelber, A., Balkenius, A. & Warrant, E. J. Scotopic colour vision in nocturnal hawkmoths. Nature 419, 922–925 (2002).
- Kyba, C. C. et al. Artificially lit surface of Earth at night increasing in radiance and extent. Science Advances 3, e1701528 (2017).
- Sanders, D. et al. A meta-analysis of biological impacts of artificial light at night. Nature Ecology & Evolution 5, 74–81 (2020).