Why all those butterflies are so cool right now

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Why all those butterflies are so cool right now

There’s a reason why all the insects delighting SA can fly so far – and their trick could be very useful to us too

Cape Town bureau chief
A brown-veined white, the butterfly that has filled the skies of Gauteng, Free State and KwaZulu-Natal this week during a migration from the Northern Cape.
small wonder A brown-veined white, the butterfly that has filled the skies of Gauteng, Free State and KwaZulu-Natal this week during a migration from the Northern Cape.
Image: commons.wikimedia.org

Butterflies have been on everyone’s lips in large parts of SA this week thanks to the mass migration that has filled the skies with brown-veined whites.

Amid the millions of butterflies fluttering northeast from the Northern Cape, it’s easy to lose sight of the small miracle that each insect embodies.

But a new study from scientists in the US has helped to restore our sense of wonder by revealing how they make minute adjustments to their wing temperatures so they perform optimally.

The scientists said their discovery, which is one of the factors allowing feather-light brown-veined whites to fly more than 1,000km between the Kalahari and the Mozambique coast, could help to design better artificial wings and even keep humans cool.

Physicists and biologists at Columbia Engineering and Harvard found wings contain a network of living cells that work best within a constrained range of temperatures.

Writing in the journal Nature Communications, they said wings could overheat rapidly in the sun when butterflies landed and could cool down too much during flight.

“Butterfly wings are essentially vector light-detecting panels by which butterflies can accurately determine the intensity and direction of sunlight, and do this swiftly without using their eyes,” said co-author Nanfang Yu, from Columbia.

Temperature distributions on the forewing of three species of butterflies illuminated by sunlight, showing that despite the wings' wide variation in visible colouration and pattern, the temperature of the scent patches, pads and wing veins that contain living cells is always lower than that of the remaining 'non-living' parts of the wings.
hot topic Temperature distributions on the forewing of three species of butterflies illuminated by sunlight, showing that despite the wings' wide variation in visible colouration and pattern, the temperature of the scent patches, pads and wing veins that contain living cells is always lower than that of the remaining 'non-living' parts of the wings.
Image: Nanfang Yu and Cheng-Chia Tsai

The scientists carefully removed scales then stained neurons inside the wings, discovering they are loaded with mechanical and temperature sensors.

They also discovered a “wing heart” that beats a few dozen times per minute to facilitate the directional flow of insect blood, or hemolymph, through a “scent pad” or an androconial organ located on the wings of some species of butterflies.

Co-author Naomi Pierce, from Harvard, said most research on butterfly wings had focused on colours, which were believed to be used in signalling between individuals.

“This work shows that we should reconceptualise the butterfly wing as a dynamic, living structure rather than as a relatively inert membrane. Patterns observed on the wing may also be shaped in important ways by the need to modulate temperatures of living parts of the wing,” she said.

The brightness in infrared photographs of butterflies correlates with the capability of radiative cooling.
cool customers The brightness in infrared photographs of butterflies correlates with the capability of radiative cooling.
Image: Nanfang Yu and Cheng-Chia Tsai

Yu’s lab used infrared imaging to measure temperature distributions over butterfly wings. Said Pierce: “This has been difficult to do until now because of the thinness and delicacy of butterfly wings.”

Yu said the technique enabled his team to examine physical adaptations beyond wings’ visible appearance, and they found a mechanism that controlled thermal radiation.

Experimental conditions that mimicked the natural environment allowed researchers to quantify the relative contributions of several environmental factors to the wing temperature. These included the intensity of sunlight, the temperature of the terrestrial environment and the “coldness” of the sky.

They found that wing areas containing live cells are always cooler than “lifeless” regions of the wing due to enhanced radiative cooling.

“The nanostructures found in the wing scales could inspire the design of radiative-cooling materials to cope with excessive heat conditions,” said lead author Cheng-Chia Tsai, from Columbia.

Yu said the team’s discovery could also help to design the wings of aircraft and other flying machines.

“Perhaps wing design should not be solely based on considerations of flight dynamics, and wings designed as an integrated sensory-mechanical system could enable flying machines to perform better in complex aerodynamic conditions,” he said.