Embedded Files
Introduction:
The Heliconius, or passion vine, butterflies are a colourful group of butterflies found in the rainforests of South and Central America. Their bright wing colours act as warnings, telling predators that they are poisonous or unpleasant to eat because of toxic compounds they produce and get from the plants they eat (the passion vines).
Different species in this group often share the same colours and patterns, and this benefits both species by making it easier for the predators to learn to avoid the pattern. Heliconius erato and Heliconius melpomene are not closely related and genetically very different, but have almost identical wing colour patterns.
Another incredible thing about these two species is that in different parts of South America they have evolved different wing colours and patterns. We have identified one of the genes that has changed between the different populations in South America to produce the differences in wing patterns, a gene called Cortex.
Peppered moth (Biston betularia). Photo by Andy Hunter, https://www.ukmoths.org.uk/species/biston-betularia/pair-in-cop/
The Cortex gene:
Amazingly, changes in Cortex were also responsible for producing black peppered moths, which spread during the industrial revolution in England, when they were better able to hide against the soot covered trees.
These results are helping us to understand why particular genes, like Cortex, seem to be particularly good at producing the variation needed for evolution to happen.
Current Research:
Researchers at the University of Sheffield are now investigating a different aspect of colour variation in Heliconius: the shiny iridescent blue colour. The difference between iridescent blue and matt black butterflies lies in tiny nanostructures on the surface of the scales that cover the wings, and the way these either reflect or absorb light.
By investigating the genes that control these nanostructures we can understand how the butterfly is able to produce them. This could lead to new technologies for producing nanostructured surfaces with a wide range of applications from solar panels to paint, bridging the gap between fundamental biological discovery and real-world innovation.
Festival of the Mind 2018 - Mimicry, Magic & Iridescence:
The Heliconius butterfly has a fascinating evolutionary story - a historic journey of mimicry and genetics. During the Festival of the Mind in 2018, visual artist Sarah Jane Palmer worked closely with the Department of Animal and Plant Sciences and The Alfred Denny Museum to discover more about this evolutionary journey and created two new artworks. These were exhibited at The Millennium Galleries during the festival and are on permanent display in the Alfred Denny Building at the University of Sheffield.
Some of Sarah Jane Palmer's artworks for the Festival of the Mind 2018. By Sarah Jane Palmer, https://sarahjanepalmer.co.uk/mystery-and-magic-of-the-heliconius-butterfly
About the artist:
Sarah Jane Palmer an artist with a passion for pattern, illusions and fantastical storytelling. From the historical Nottingham lace trade to the romance of the circus, her film, animations and designs for wallpaper and textiles draw from her fascination with archive images, historical research and visual trickery. More of Sarah Jane Palmer's work can be viewed on her website (https://sarahjanepalmer.co.uk/).
"It's amazing how different patterns can be drawn upon. I often get immersed in things that - when seen from one angle and glanced from another - can look completely different. Like the iridescence in a butterfly's wing, my artworks explore the difference between a gaze and a glance." - Sarah Jane Palmer
PhD Research, Sonal Ladwa:
Sonal Ladwa is a PhD student studying the ecology, evolution and biophysics of tropical butterfly wing colouration and colour-producing nanostructures at University of Sheffield and Natural History Museum London. Her research interests include entomology, ecology, natural history and optics. Sonal's current research focuses on the optical and thermoregulatory properties of tropical Nymphalid wings. She is funded by the NERC ACCE DTP studentship.
1. Tropical environments and colourful butterflies
Tropical forests are home to some of the world's most colourful and diverse butterflies. These environments are incredibly rich in species because they offer a huge variety of habitats, from cool, misty mountain cloud forests to the warm, humid lowlands and from the dark forest floor to the bright, sun-filled canopy above.
A Global Hotspot of Butterfly Diversity
Butterflies in the family Nymphalidae (brush-footed butterflies) are especially diverse and are found in all zoological regions of the world, except Antarctica. They make up nearly a third of all butterfly species worldwide and 43.4% of the planet's Nymphalid species are found in South America, particularly Columbia, Ecuador, and the Andes. The Andes, the longest mountain range on Earth, create a complex landscape of changing temperatures, vegetation, and light xonditions. These environmental differences help generate and maintain the extraordinary variety of butterfly species found there.
Click to read more...
Butterflies and Their plants
Butterflies have evolved alongside the plants they feed on for millions of years. Host plant variation is important as adult butterflies choose where to lay their eggs based on habiotat conditions and plant availability, where the hatched caterpillars rely on these host plants for food. Making host plant availability in the envrionment particulalryl important to butterfly distribution. As plant abundance changes with altitude, light, and humidity, and acroos environments, butterfly communities shift too. Where plants thrive, butterflies tend to follow.
How Habitat Shapes Butterfly Communities
Altitude dramatically alters climate:
Low elevations are warmer, more humid, and often host a greater variety of plants.
High elevations are cooler, wetter, and more exposed to wind and weather, supporting fewer species adapted to these harsher conditions.
These differences meant that butterfly communities often change as you move up a mountain. But vertical differences within the forest matter too. Tropical are layered:
The understory is cool, dark, and sheltered.
The canopy is bright, hot, and exposed, with far more sunlight and UV radiation.
Because of these contrasting environments, some butterflies prefer the calm, shaded understory while others thrive in the sun-drenched canopy. Light levels, temperature, plant availability, predators, and even signalling opportunities. All of these factors help determine where different butterfly species live.
Why this matters
Butterfly communities are shaped by a mix of climate, vegetation, and behaviour. These pressures affect everything from their wing colours to their ability to thermoregulate, fly, and reproduce. By studying how butterflies are distributed across altitude and forest layers, we can better understand how tropical biodiversity is structured and how environmental change may alter these intricate patterns.
Butterfly Colour and Thermoregulation
Butterflies are known for their striking and diverse colours, which are not only beautiful but also play important roles in communication, camouflage, and even temperature regulation. In the tropics, where light and temperature can vary dramatically from the dark forest floor to the sun-filled canopy, colour can be a crucial part of how butterflies survive.
Why Colour Matters
Butterfly wings interact with light in three major parts of the spectrum:
UV and visible light – used for signalling to mates, confusing predators, or blending into the environment
Infrared light (IR) – not seen by most animals, but important for heating and cooling
Because solar radiation includes all three, a butterfly’s colour can influence both how it is seen and how it manages heat.
Pigments, Heat, and the Problem of Staying Warm
Pigments such as melanin don’t just create dark colours but they also absorb heat. Darker butterflies often warm up faster in cooler environments, a pattern known as thermal melanism. This has been observed in many insects, birds, and reptiles. For butterflies living at higher, cooler altitudes or in shadier habitats, being darker can give them a thermal advantage by helping them get up to flight temperature more quickly. Melanin also absorbs ultraviolet light, offering protection in environments with strong sunlight, such as high mountains.
Iridescence and Hidden Colours
Some butterflies get their colour not from pigments, but from tiny nanostructures in their wing scales. These structures reflect and interfere with light to produce brilliant blues, greens, and metallic sheens, that we call structural colour. These same nanostructures also influence how wings reflect or absorb infrared light. That means iridescent butterflies might heat up differently from non-iridescent species, even if they look bright or reflective in visible light. In some species, pigments and structures interact, creating colours that serve multiple functions at once.
Colour, Climate, and Habitat Choice
Thermoregulation is essential for butterflies, which rely on external heat to fly. In a tropical forest, temperatures and sunlight can shift dramatically depending on altitude and whether a butterfly is in the understory or canopy.
The understory is cooler, darker, and more stable.
The canopy is brighter, hotter, and more exposed to sun and UV radiation.
Butterflies can move between these microhabitats to regulate their body temperature, but their wing colours and structures may also help them tolerate particular environments. For example, a butterfly living in the bright canopy might evolve colours that prevent overheating, while an understory species might benefit from colours that help it warm up more quickly.
What We Still Don’t Know
Although many studies have explored colour in temperate butterflies, much less is known about how colour works for the diverse species living in tropical rainforests. We don’t yet fully understand how pigment, structural colour, and infrared reflectance together influence where tropical butterflies live.
Figure 1: Composite multispectral images of Batesia hypochlora (Natural History Museum, UK). Panels show dorsal (d) and ventral (v) sides in the (A) visible spectrum, (B) infrared spectrum, and (C) ultraviolet spectrum. Dotted white lines indicate the wing vein boundaries that are consistent in all butterflies.
Figure 2: Prepona meander, a nymphalid butterfly, a zoom into the pigmented black and structural coloured, iridescent scales on the image and an iridescent patch viewed under a light microscope.
Figure 3: A: The four trapping sites in Ecuador: Yasuni National Park, 250m; Wildsumaco Lodge, at 1500m; Mashpi Rainforest Reserve , 900m and El Durango, 400m, courtesy Patricio A. Salazar.. B: An illustration of the trapping positions for each trap pair in the understory and the canopy, and the median distance from the ground (in meters).
2. How Tropical Butterflies Stay Cool (or Warm) Across Changing Forest Environments
Tropical rainforests create a surprising mix of climates. Higher altitudes are cooler but receive much stronger sunlight, while the lowlands are warmer but more shaded. For butterflies, animals that rely on external heat sources to warm up, these shifting conditions pose major challenges. How do they keep their bodies at the right temperature to fly, forage, and survive?
Our research explored how butterflies handle heat across different altitudes and forest microhabitats, revealing a complex mix of passive (sun-driven) and active (behavioural or physiological) thermoregulation.
Click to read more...
How Wings Heat Up: Passive Temperature Gain
To test how a butterfly would warm up without using its muscles or behaviour, we placed mounted butterfly wings in either direct sun or under forest cover at different altitudes.
We found that wings heat up much faster in open sunlight than under canopy cover. This difference becomes even stronger at higher altitudes, where sunlight is more intense. As a result, wings at high altitude reached temperatures above the surrounding air much more quickly than wings at lower altitude. These patterns reflect the powerful role of solar radiation at high altitudes, a factor that is often overlooked when considering how temperature changes with altitude.
Live Butterflies Tell a Different Story
We also measured the body (thorax) temperatures of live butterflies caught at different altitudes and microhabitats. The results were the opposite of what the wing experiments predicted: Butterflies at higher altitudes were cooler relative to the air than those at lower altitudes. Whether a butterfly was caught in open sun or under the canopy did not affect its body temperature. Live butterflies had thoracic temperatures consistently warmer than the air, even warmer than the sun-heated wings. This tells us that butterflies aren’t just passive solar collectors, they also use active mechanisms such as muscle-generated heat or behavioural strategies to regulate their temperature.
Putting It Together
Tropical butterflies appear to combine passive and active thermoregulation to cope with changing climates across the forest. They warm up using sunlight when possible, but they can also adjust behaviorally or physiologically when sunlight is limited or when temperatures drop at higher altitude. This means that predicting how butterflies, and possibly other tropical ectotherms, will respond to climate change requires understanding both air temperature and solar radiation, especially across altitudinal gradients.
Figure 4: An example of butterfly “models”, used to measure temperature. The images show just the left side of the model for a) H. erato and the right side of the b) H. sara model. The blue spots represent the area of the wing that were measured with the thermocouple.
3. Colour, Heat, and Habitat: Wing Pigmentation and Structural Colour in Heat regulation and Signalling
Tropical forests have distinct vertical layers, from the dark understory to the bright, hot canopy. These layers create unique light and temperature environments that shape where different butterfly species live. Using museum specimens from 148 Neotropical butterfly species, multispectral imaging, and optical measurements, we studied how wing colour, pigmentation, size, and structural features vary between canopy and understory species.
Click to read more...
Pigmentation Is Shaped by Microhabitat, Not Just Altitude
Instead of a simple “higher altitude = darker wings” pattern, we found that microclimatic habitat use (canopy vs. understory) was much more important in determining wing coloration. Canopy species have darker wings, which helps reduce glare and may improve heat absorption in bright, hot environments. Understory species were generally lighter, reflecting the cooler, dimmer conditions. These differences don’t always match classical predictions of “thermal melanism,” showing that colour evolution in the tropics is shaped by more than just temperature.
Iridescence Changes How Wings Absorb Heat
One of our most surprising findings is that structural colours, especially iridescence, can change how wings absorb heat. Iridescent species had lower infrared reflectance, meaning they absorb more heat in the infrared range than expected based on visible colour alone. This suggests that nanostructures, not just pigments, play a key role in thermoregulation. In other words, butterfly colours can influence heating in ways our eyes can’t see.
A Multifunctional Colour System
Across the visible, UV, and infrared ranges, we found that wing coloration serves multiple roles:
Thermoregulation: controlling how wings absorb or shed heat
Signalling: attracting mates or warning predators
Camouflage: blending into specific microhabitats
Together, these functions shape the evolution of wing colour across vertical forest strata.
Why This Matters
Understanding how butterflies balance heat, light, and communication in such a complex environment helps us predict how tropical species will cope with environmental changes. Their colour patterns are more than just decoration; they are finely tuned adaptations to the forest’s vertical world.
Figure 4: Phylogenetic tree of 148 nymphalid butterfly species. Tips are coloured by iridescence (blue = iridescent, black = non-iridescent). Concentric rings show dorsal reflectance and vertical stratification: inner to outer rings — visible (black = low, white = high), infrared (red = low, yellow = high), ultraviolet (dark blue = low, light blue = high), and stratification preference (dark green = understory, light green = canopy). Subfamilies are indicated, and a representative species is shown.
Photos: Data collection involved taking multispectral images of butterflies in the Natural History Museum, London.
Page updated
Report abuse