Most beekeepers rate Varroa destructor mites as biggest threat to their honey bees (Apis mellifera). Shown here is a honey bee with two Varroa mites, one on the side of the bee’s abdomen near its legs and one atop the abdomen. A new study shows storing honey bee colonies with elevated levels of carbon dioxide reduces levels of Varroa mites, a method that might prove useful in reducing beekeepers’ winter colony losses. (Photo by USGS Bee Inventory and Monitoring Lab via Flickr, public domain)