Stag beetle larvae feed on rotting wood. Wood is plentiful and contains mostly carbohydrate useful for providing energy but many other essential nutrients are present only in small concentrations. Wood feeding insects often harbor microorganisms that can aid in digestion and synthesize nutrients that insects cannot.
Female stag beetles (Lucanidae) have an invagination of their abdominal cuticle that contains yeast. This mycangium is only present in females and is absent in the males. The females transport the yeast to their galleries in the wood and pass them to their larvae. The larvae have no specialized structures but the yeast can attach to the gut walls to prevent dislocation during feeding.
Some of the yeast may be only found in association with insect. The yeast are capable of survival on a number of sugars associated with wood. As our ability to study microorganisms improves the importance of insect microbe interactions becomes apparent.