Animals and plants host communities of bacteria and other microorganisms—known as microbiomes—that are essential for health. A central goal of microbiome science is to discover what causes the microbiome to change, and the broader consequences of such change. A consistent pattern emerging from this research is that the microbiome is seasonal: an animal in spring, for example, will have a very different microbial makeup from one in fall. But what causes the microbiome to change? And do seasonal microbiome changes influence the timing of critical biological events, such as hibernation? Answers are urgently needed, because increasingly erratic and extreme weather is knocking the life cycles of animals and plants out of sync, and in turn, jeopardizing wildlife populations and the many services they provide to society. How the microbiome is involved, and how it may be harnessed to maximize the stability of natural and agricultural ecosystems, are currently unknown. This project will focus on these open questions through experiments and field studies involving bumble bees. General principles resulting from this research will ultimately improve prediction and management of microbiome change in wildlife. Further, findings will inform specific strategies to protect bumble bees, a threatened group of pollinators that is vital for agriculture. This project will also support educational initiatives designed to help grow the science and technology workforce. The researchers will train tea