Without oxygen, we'd be in big trouble. The gas, which makes up 21 percent of Earth's atmosphere, keeps alive the cells that make up our bodies. But there's such a thing as too much oxygen. Extra oxygen can damage tissues.

Insects need oxygen to live, too, and they can also get too much. Two researchers now propose that many ants, grasshoppers, moths, and other insects sometimes stop taking in oxygen for hours or even days at a time to avoid overdosing.

Insects breathe through little holes, or spiracles, that line their bodies. Oxygen enters through the spiracles, which lead to branching airways. Oxygen travels through these tubes to different parts of an insect's body and diffuses into the blood and gets used by cells. The cells release carbon dioxide, which is carried back to the spiracles.

Insect spiracles can open and close. Scientists had suggested that this opening and closing of air holes helps prevent water loss. Stefan K. Hetz of Humboldt University in Berlin and Timothy J. Bradley of the University of California, Irvine now propose that insects do it to keep their tissues from getting too much oxygen.

An insect's airways can deliver oxygen 200,000 faster than the blood vessels of mammals typically can, and they whisk away carbon dioxide about 10,000 times faster. All of this oxygen exchange could harm an insect's cells and tissue.

To investigate this idea, the researchers inserted measuring probes into spiracles of Atlas moth pupae. The pupa is the stage at which the caterpillar wraps itself in a covering and, hidden away, turns into a moth. The researchers then varied the concentration of oxygen in the environment.

The results showed that oxygen concentrations inside the airways of the moths stayed the same, even when oxygen concentrations outside of their bodies varied quite a bit. This finding suggests that the insects close their spiracles to avoid getting too much oxygen, the researchers say.

Insects seem to be able to make sure they get just the right amount of a good thing.—E. Sohn