X-ray scans look at changes inside a chrysalis

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Scientists have recorded the intimate changes involved when a caterpillar transforms into a butterfly.

Researchers used micro-CT scans to look inside a chrysalis during the process of metamorphosis.

A series of images revealed how the caterpillar's breathing tubes altered to become the intricate respiratory system of a butterfly.

The assembled footage features in the BBC Four documentary Metamorphosis: The Science of Change.

"We use this 3D imaging technology in archaeology to analyse the internal structure of objects such as bones and pottery, but it works just as well for small bodies with complex internal anatomy like a chrysalis," said archaeologist Professor Kate Robson Brown, from the University of Bristol, who was part of the team that undertook the study.

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The researchers scanned three stages in the life cycle of the blue morphos (Morpho menelaus) butterfly: a caterpillar one day before metamorphosis, a week-old chrysalis and a chrysalis one day before the butterfly emerged from within.

They used micro-CT (computerised tomography) technology, firing x-rays at the insects to generate a computer image of their insides.

Professor Duncan Bell, from the University Campus Suffolk, then led the team to "digitally dissect" the images. They used software to strip away the layers of tissue on the computer model so they could focus on changes to the respiratory system.

Finally biologist Dr Mark Greco, from the University of Bath, assembled the images into a film. He is pioneering the method, referred to as Diagnostic Radioentomology (DR), to visualise the internal organs of insects in 3D.

"The fact that it is non-invasive means that we can dissect an insect without touching it," explained Dr Greco.

"All other methods are either destructive, take too long or they are not sensitive enough. DR can be done on live, valuable or rare insects without harming them."

A 3D caterpillar before dissection A virtual caterpillar before dissection

Although they expected "dramatic" changes in the insects' internal structure, the team were surprised by the speed of the transformation.

"The changes that happened to the breathing apparatus, most of them happened by the time we took that second scan," explained Dr Greco.

"In future studies we'll scan every day to watch those changes."

He suggested that such speed could be motivated by the perils of being a stationary target.

"During metamorphosis the insect is quite vulnerable - it can't escape predators... I think it becomes an adult very rapidly so it might stand half a chance," Dr Greco told BBC Nature.

Metamorphosis: The Science of Change broadcasts on BBC Four, Wednesday 13th March at 2100 GMT as part of the Alien Nation season.

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