Fat bodies are not the same as “body fat.” They are organs that contain a conglomeration of protein and fat and act similarly to the liver in mammals. They perform many diverse tasks in the bee’s body, including pesticide detoxification and immune function.
Because they store large amounts of protein, fat bodies are also essential for long-lived healthy bees, because older workers rarely consume additional protein. Those that are foragers almost never do.
The role of this biological structure was not fully elucidated until 2018, when Dr. Samuel Ramsey first presented the results of his vital experiments that overturned the long-standing orthodoxy that the mite, Varroa destructor, feeds on bee blood (hemolymph). His research proved that instead, these mites feed almost exclusively on honey bees’ fat bodies — with grave consequences to the targeted individuals and their entire colony.
For more detail of Dr. Ramsey’s pioneering work on fat bodies and the feeding behavior of Varroa destructor, watch his 2018 presentation to a group of beekeepers.
Visit this link to read Dr. Ramsey’s more detailed technical report, “Varroa destructor feeds primarily on honey bee fat body tissue and not hemolymph,” published in the Proceedings of the National Academy of Sciences (2019).