Insects don't have lungs, so how do they breathe? Using tiny air sacs no-one even knew existed, according to American scientists who have taken the first close-up views of the process.

It took one of the world's most powerful X-ray machines - generating an image hundreds of times more detailed than the most sophisticated medical scans - for scientists at The Field Museum and Argonne National Laboratory, both in Chicago, to see how beetles, crickets and ants breathe.

"They are really pumping some gas," said Dr Mark Westneat, a curator of zoology at the museum and leader of the study.

While resting, the insects exchanged up to half the air inside their main oxygen tubes every second, equivalent to how hard a person breathes while doing moderate exercise, the researchers report in today’s edition of the journal Science.

The tubes, called tracheae, connect to tiny air holes in the insect's outer coating. For decades, scientists had thought that air passively oozed into those holes. Then researchers spotted some tiny air sacs near insects' wings, legs and abdomens that they might use to help pump air inside.

But the rest of the insect body is rigid, no one thought much more air pumping could go on. Instead, Westneat discovered insects somehow squeeze the air tubes throughout their bodies to suck air in and out, much as lungs do. "It's an important discovery," said entomologist Dr Robert Dudley of the University of California, Berkeley.

Equally important was the synchrotron used to reveal the insectoid breathing trick. The large particle accelerator generates the world's most intense X-rays, and there are very a few like it in existence, mostly used in chemistry, Westneat said.

And it’s use emerged by accident: Argonne physicist Dr Wah-Keat Lee had been looking for new ways to use the synchrotron. When he placed a dead ant inside the machine, he saw spectacularly detailed images of its organs.

Teaming up with Westneat, he began to put living insects in the synchrotron, bombarding them with massive doses of radiation in order to get spectacular images.

"What we've done with this work is created a window into these tiny little animals that nobody's ever seen inside before," said Westneat. The duo next hope to use the synchrotron to study how insects eat and how the multiple hearts of beetles function.

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