Olfactory carbon dioxide detection by insects and other animals.

Carbon dioxide is a small, relatively inert, but highly volatile gas that not only gives beer its bubbles, but that also acts as one of the primary driving forces of anthropogenic climate change. While beer brewers experiment with the effects of CO2 on flavor and climate scientists are concerned with global changes to ambient CO2 levels that take place over the course of decades, many animal species are keenly aware of changes in CO2 concentration that occur much more rapidly and on a much more local scale. Although imperceptible to us, these small changes in CO2 concentration can indicate imminent danger, signal overcrowding, and point the way to food. Here I review several of these CO2-evoked behaviors and compare the systems insects, nematodes, and vertebrates use to detect environmental CO2.