MSUE Diagnostic specimen: Hermit flower beetle grub

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.   

This giant grub came out of a “chocolate egg” pupal case when we broke it open. The thin-walled “eggs,” which could pass for fecal pellets of some very large rodent-like creature, are made by the grub for its last winter before changing to a pupa and then emerging as an adult hermit flower beetle. They were falling out of an oak tree and this is one of the smaller ones, according to the gardener who brought it in. They suspected some squirrel may have been cleaning out the tree hollow they grew up in, or how else could they have fallen?

The large scarab beetles are occasionally found on flowers as adults but are not pests. The larvae feed only on rotting wood or associated fungi, etc., and are found in tree hollows and rotting stumps, where the eggs are laid by the adult beetles after mating. They are called hermits apparently because so much of their life is spent hiding in such places. You can see a photo of the adult on this page,
with rearing instructions. Monroe MSUE secretary Diane Michaud gasped “Why would anyone want to raise them?!”

Hermit flower beetle grub.
Photo 1. Hermit flower beetle grub.

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