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.