Aristotle erred; super X-ray proves insects do breathe
The discovery may seem small, and by some measures it is. Exposing insects to X-ray beams 1 billion times more powerful than ones used by doctors, scientists have observed pulsing, lunglike structures that typically are smaller than the commas in this sentence.
Evidence that insects actively inhale and exhale is nothing less than historic for biologists, closing the books on a debate that dates to Aristotle, who grudgingly conceded insects are alive but scoffed at the idea they could breathe.
"We could watch the tracheal tubes in the head and thorax, which are not squishy parts of the body, really squeezing and releasing," said Mark Westneat, of Chicago's Field Museum, who led the study. "They're not lungs, but they're lunglike."
The discovery, Westneat said, could lead to new insecticides, including perhaps some that kill insects by asphyxiating them, and the X-ray technology might be adapted for medical imaging in people.
Until recent decades, entomologists hewed largely to Aristotle's view, believing air simply drifted into and out of tiny holes in insects' bodies. More recently, it became clear insects pump air through these holes by moving their bodies in particular ways.
Only now is it clear that insects — like people — use muscles specifically to inhale and exhale, even when the creatures are outwardly still.
Indeed, scientists said, there's even emerging evidence that insect breathing is synchronized with the pulsing of the creatures' circulatory systems, a level of physiological sophistication few had imagined.
"It looks like there's a very complicated neurological system to keep all this coordinated," said Thomas Miller, an insect physiologist at the University of California, Riverside.
"The insect body is starting to look more and more like the vertebrate body all the time in terms of what really drives things."
Scientists long have known that insects have holes in their bodies that lead into sinuslike pouches or tubes, bringing oxygen from outside air to the fluids and tissues inside a bug's body and allowing carbon dioxide to find its way back into the atmosphere.
Also clear was that some insects can expand and contract their abdomens to force extra doses of air through those holes — in effect, pant.
Evidence in recent years had suggested insects might be capable of more than that, but it's not easy to document insect inhalation. And the scientist who has been the most vociferous advocate for bug breath — Karel Slama, of the Czech Academy of Sciences in Prague — is such an outspoken, flamboyant character (some scientists have called him a "pest") that his work largely has been ignored.
What did it take to prove Slama right? An enormous particle accelerator called a synchrotron: a circular tunnel more than one-half mile around through which electrons are sent hurtling at nearly the speed of light.
The synchrotron that Westneat used, part of the Energy Department's Argonne National Laboratory in Illinois, is the most powerful X-ray machine in the Western Hemisphere.
The project started one day when Argonne scientist Wah-Keat Lee and a postdoctoral student took aim at the head of a dead ant found in the lab.
"We looked at its head, and it was quite astounding," Lee said. "I thought, 'Somebody's got to be able to do something good with this.' "
He contacted Westneat, who jumped at the opportunity. The team soon was taping grasshoppers, beetles, dragonflies, silverfish, flies and ants to microscope slides and creating highly detailed videos of their respiratory organs.
"We used one of the biggest scientific tools in the world to look at one of the smallest animals on earth," Westneat said.
A preliminary analysis of the work, published in today's issue of Science, suggests insects' muscles squeeze out about 50 percent of the gas in their air tubes every second or so — roughly equivalent to what a person does while walking fast or going on a short jog.
That's probably a bit faster than the normal resting rate, Westneat said, given that bugs in the experiment probably were in a panic while taped to a slide.
"We think the rates we're seeing are similar to those in insects during exercise or flight, because they're under some degree of stress," he said.
Insects appear to contract their muscles to exhale, and inhalation happens effortlessly in a rebound effect. That's the opposite of how breathing works in people, where diaphragm muscles do their work during inhalation.
"Insects never cease to amaze with their capacity to do a lot with the little that they have," said May Berenbaum, an entomologist at the University of Illinois, Urbana-Champaign. "We were clearly mistaken to underestimate the capacity of their tracheal respiratory system."
Westneat and Lee are trying to learn how insects chew their food by focusing on insect mouth parts that until now have been impossible to watch in real time.