Text and photographs by Jacqueline Garget
Pollen-eating Heliconius butterflies have remarkable powers of learning and memory. Professor Steve Montgomery is investigating what this can tell us about the evolution of brains and behaviour.
Have you ever wondered how long a butterfly lives? For many species, it’s just a few short weeks. That’s because when the adult emerges from the chrysalis it has no means of eating anything nutritious; it instantly starts burning through the protein it stored as a caterpillar and when it’s gone, it’s gone.
“Nectar tends to be rich in sugar but very poor in protein,” says Professor Steve Montgomery in the Department of Zoology, “so most butterflies have to use what they ate as a caterpillar to repair their tissues and to reproduce. Once they run out of protein, they’re dead.”
Montgomery is studying butterflies that have found a way around that trap. Heliconius are a colourful butterfly group from the American tropics, and they’ve developed an unusual behaviour: they collect and eat pollen.
A butterfly’s proboscis – the long, tube-like mouthpart – is generally used like a drinking straw to suck nectar from flowers. Heliconius uses it like a sophisticated food processor.
“Heliconius have a long lifespan, especially when you consider that they don’t sleep over the winter in the tropics. Some can live for up to five to six months – and in a recent study we had one that almost made it to a year,” he says.
“They manage to live so long because they collect big clumps of pollen, and slowly digest them by releasing saliva and rolling them back and forth with the proboscis. That grinds up the pollen, everything goes into solution, and the butterflies can then suck it up.”
Being able to get protein as adults, and consequently live much longer, has transformed the biology of these butterflies – raising questions that keep Montgomery, who initially set out to study primates, absolutely fascinated.
Finding his wings
Montgomery was an undergraduate and PhD student at Cambridge, and has since worked at University College London, the University of Bristol, and the Smithsonian Tropical Research Institute in Panama. He returned to Cambridge this year to take up the Prince Philip Professorship of Ecology and Evolution.
“I was originally investigating brain evolution in primates,” he says, “and as an early-career researcher I was looking for a model species for my experiments, to try and understand how our brains evolve and how that impacts our behaviour.”
After learning about his colleague Professor Chris Jiggins’ work on butterfly wing patterns, Montgomery wondered whether Heliconius butterflies might be the answer. He found a research paper from the 1980s describing the ‘mushroom body’ of Heliconius as particularly large compared to three other species of butterflies. So-called because it looks like a tiny mushroom, this is the part of a butterfly’s brain where learning and memory occur.
With a promising model species identified, Montgomery set out to map the anatomy of the mushroom body to better understand Heliconius brain wiring and how it develops. At the other end of the scale he started looking at the insect’s behaviour, to see how the two might be connected.
“In butterfly terms Heliconius have massive brains, with around eight times more wiring in their mushroom bodies than their closest butterfly relatives,” says Montgomery.
“I want to understand how this expansion came about, and how the mushroom body has become specialised to process visual and spatial information.”
When a butterfly starts depending on pollen for survival, it needs to develop ways of remembering where the right plants are, and when they’ll be flowering. Montgomery thinks this new behaviour could help explain the extraordinary changes in the butterfly brain.
Working with collaborators at the Smithsonian Tropical Research Institute in Panama, he and a talented team of postgraduate students and post-docs have carried out experiments comparing the cognitive abilities of various butterfly species. These showed that Heliconius outperform their closest relatives in specific learning and memory tasks, strengthening the idea that their unusual brain anatomy and pollen-feeding lifestyle evolved hand in hand.
Bringing the tropics to Cambridge
Joining the University of Cambridge brings Montgomery much closer to the broad range of expertise – in neuroscience, developmental biology, and more – he needs to progress his work. “There are things I hope to investigate in Cambridge that I just couldn’t do anywhere else,” he says.
Unlike in Panama, raising tropical butterflies and the plants their caterpillars eat in Cambridge depends on specialist facilities: large greenhouses kept at 28oC, with high humidity and a lighting pattern to mimic tropical days and nights.
Already Montgomery is brimming with new research questions: what makes one butterfly species grow a bigger mushroom body than another? If he can change how that brain region develops, will it change what a butterfly can learn?
His ultimate aim is to understand how brains evolve and how that impacts behaviour, and how both of these factors can drive the evolution of new species. It’s a huge quest, rooted in a fundamental curiosity about life.
With so much butterfly biology to explore, will he go back to studying the primates one day? “No, it’s too restrictive!” he says. “Even though they’re tiny little butterflies, studying them makes it far easier to integrate the different questions I’m interested in. I’m going to stick with them.”
Published 5 October 2026
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source: cam.ac.uk