[Editors] MIT shows how insects breathe underwater

[Teresa Herbert]

For Immediate Release
WEDNESDAY, JUL. 30, 2008

Contact: Teresa Herbert, MIT News Office
T. 617-258-5403   E.: therbert at mit.edu

PHOTO AVAILABLE

======================================
Life in a bubble
--Research shows how insects use trapped oxygen to breathe underwater
======================================


CAMBRIDGE, Mass. -- Hundreds of insect species spend much of their  
time underwater, where food may be more plentiful. MIT mathematicians  
have now figured out exactly how those insects breathe underwater.

By virtue of their rough, water-repellent coat, when submerged these  
insects trap a thin layer of air on their bodies. These bubbles not  
only serve as a finite oxygen store, but also allow the insects to  
absorb oxygen from the surrounding water.

“Some insects have adapted to life underwater by using this bubble as  
an external lung,” said John Bush, associate professor of applied  
mathematics, a co-author of the recent study.

Thanks to those air bubbles, insects can stay below the surface  
indefinitely and dive as deep as about 30 meters, according to the  
study co-authored by Bush and Morris Flynn, former applied mathematics  
instructor. Some species, such as Neoplea striola, which are native to  
New England, hibernate underwater all winter long.

This phenomenon was first observed many years ago, but the MIT  
researchers are the first to calculate the maximum dive depths and  
describe how the bubbles stay intact as insects dive deeper  
underwater, where pressure threatens to burst them.

The new study, which appears in the Aug. 10 issue of the Journal of  
Fluid Mechanics, shows that there is a delicate balance between the  
stability of the bubble and the respiratory needs of the insect.

The air bubble’s stability is maintained by hairs on the insects’  
abdomen, which help repel water from the surface. The hairs, along  
with a waxy surface coating, prevent water from flooding the spiracles— 
tiny breathing holes on the abdomen.

The spacing of these hairs is critically important: The closer  
together the hairs, the greater the mechanical stability and the more  
pressure the bubble can withstand before collapsing.

However, mechanical stability comes at a cost. If the hairs are too  
close together, there is not enough surface area through which to  
breathe.

“Because the bubble acts as an external lung, its surface area must be  
sufficiently large to facilitate the exchange of gases,” said Flynn,  
who is now an assistant professor of mechanical engineering at the  
University of Alberta.

The researchers developed a mathematical model that takes these  
factors into account and allows them to predict the range of possible  
dive depths. They found that there is not only a maximum depth beyond  
which the bubble collapses, but a minimum depth above which the bubble  
cannot meet the insect’s respiratory needs.

Though the researchers found that the insects can go as deep as 30  
meters below the surface, they rarely venture deeper than several  
meters, due to environmental factors such as amount of sunlight,  
availability of prey and the presence of predators.

The researchers first took an interest in the external lung phenomenon  
when they accidentally captured one of the underwater breathers while  
looking for water striders. A few years ago, Bush and colleagues  
figured out how the striders use surface tension to glide across the  
water’s surface.

Other researchers have explored systems that could replicate the  
external lung on a larger scale, for possible use by diving humans. A  
team at Nottingham Trent University showed that a porous cavity  
surrounded by water-repellent material is supplied with oxygen by the  
thin air layer on its surface. The surface area required to support  
human respiration is impractically large, in excess of 100 square  
meters; however, other avenues for technological application exist.  
For example, such a device could supply the oxygen needed by fuel  
cells to power small autonomous underwater vehicles.

The research was funded by the National Science Foundation.

By Anne Trafton, News Office

# # #

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.mit.edu/pipermail/editors/attachments/20080730/2ed57db8/attachment.htm