The beetle presses the elytra a little more firmly against the abdomen, making its air supply visible as a bubble at the tip of the abdomen. In this way, the exchange of carbon dioxide in the breathing air with oxygen from the water is promoted. Many diving beetles do this from time to time in order to stay underwater longer, especially when they feel it's not save to go to up to the surface. By alternately increasing and decreasing the space between the abdomen and the elytra, the beetle can pull in, or push out the bell as needed.

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