Another October Orange and Black Beetle (and a note on the bubble behind)

Disintegrated Diving Beetle with Breathing Bubble, Homer Lake Wetland, October 16, 2021

Another predaceous diving beetle suitably colored orange and black for the month of October! Like one of the two beetles featured in the orange and black post last week, this is another one of the 600 species of predaceous diving beetles found in North America. It was a bit larger than the two featured last week, but only by a couple of millimeters, being perhaps six or seven millimeters long (still less than half an inch).

Notable in the photo above is the bubble on its behind. Like the other beetles last week (and the giant water scavenger beetle I wrote about half a year ago in April and many, but not all, of the other aquatic insects we've seen), these beetles breathe air and carry their air supply with them when they go underwater. Their bodies are uniquely adapted for this purpose. It may seem a bit awkward to drag an air bubble around on your behind, but this actually serves an important purpose. In addition to providing the oxygen contained in the air bubble, the bubble exposed to the water actually replaces oxygen as it is used up with oxygen that is dissolved in the water. As the concentration of oxygen in the air bubble decreases to a level less than the concentration of oxygen dissolved in the water, oxygen dissolved in the water passes into the bubble. Conversely, carbon dioxide that accumulates in the bubble passes into the water due to the difference in concentration. This does not go on indefinitely, but it does extend the amount of time these insects are able to stay submerged. Amazing!

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