INSECTS do not breathe in quite the way we thought. The revelation has caused a sharp intake of breath among zoologists, because after centuries of study it means we may have to rethink our ideas about insect physiology.
Insects take in air through holes called spiracles along their flanks, which link to a branched network of tubes, or tracheae, that carry it deep into the body. For many years, biologists believed that air diffused passively through the tracheae.
More recently, it was found that insects can draw air in through their tracheae by flexing their abdomens and making other large body movements. But till now no one had managed to peer through the creatures鈥� thick exoskeletons to study breathing in more detail.
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To overcome this, a team led by zoologist Mark Westneat at the Field Museum of Natural History in Chicago trained one of science鈥檚 largest tools on some of nature鈥檚 smallest animals. They used a giant particle accelerator at the nearby Argonne National Laboratory to shine a high-intensity X-ray beam through the exoskeletons of beetles, ants, crickets and other insects.
The X-rays revealed that the insects actively squeeze and release the tracheae in their head and thorax like tiny bellows. This pumping action can exchange nearly half of the air in their main tracheal tubes within a second or two (Science, vol 299, p 558). Westneat does not know what causes the compression, which occurs without any obvious body movements. His guess is that it may be driven in part by tensing the jaw muscles, since tracheae found in the head run directly through these muscles (see Graphic).
鈥淣obody ever suspected anything like this was going on,鈥� says Michael LaBarbera, an invertebrate zoologist at the University of Chicago. 鈥淲e don鈥檛 yet understand its significance, but you can be assured the implications will be interesting.鈥�
For instance, the breathing mechanism could mean that insects deliver more oxygen to their active muscles and nervous tissue than we thought, says Robert Dudley, a comparative physiologist at the University of California at Berkeley. In the past they may have used this trick to evolve different ways to move about on land and in the air.
The X-ray technique may also prove useful in uncovering other previously hidden aspects of insect biology, such as how insects use their fabulously complex genitalia during copulation.