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Hermit Flower Beetle

Osmoderma eremicola[3]

The hermit flower beetle is a one-inch, dark brown to mahogany scarab that is attracted to lights in July and August; its large grubs live only in rotting wood and it is harmless.[1][2]

Group
Insect
Order
Coleoptera
Family
Scarabaeidae
US records
26 states
Sources
3 cited
Updated
2026-10-16
Hermit flower beetle, a large dark brown scarab
Hermit flower beetle, a large dark brown scarab. (c) Don, some rights reserved (CC BY) — via iNaturalist, CC BY 4.0
On this page
  1. Identification
  2. Look-alikes
  3. Where it lives
  4. Biology
  5. Damage and signs
  6. Health risk
  7. Control
  8. Related profiles
  9. Common questions
  10. Sources

How to identify it

  • Adults are about 1 inch long and dark brown to black or mahogany, like a June beetle but less oval and flat on top.[1][2]
  • Larvae are large, C-shaped, dirty-white grubs with a reddish-brown head and six legs; Iowa State gives up to 1 1/4 inches long, UMN up to 2 inches.[1][2]

Look-alikes

Look-alikeHow to tell them apart
June beetlesMore oval; the hermit flower beetle is flatter on top.[1][2]
Grapevine beetleTan with black spots rather than dark brown.[1]

Where it lives

Three Osmoderma species occur in North America; Osmoderma eremicola is the most common in Minnesota and is found in Iowa.[1][2]

US map: public records from 26 states since 1990 (GBIF).

Biology and life cycle

Adults are present from July to September and are strongly attracted to lights at night.[1][2]

Grubs develop in tree cavities and very rotted stumps and logs and are found from August through the next spring.[1][2]

Damage and signs

  • The grubs are not tree pests: they arrive only after a tree is dead or weakened and its wood is decaying, and they help decompose the wood.[1][2]

Health risk

None to people or pets.[2]

Control

Prevention

No control is needed.[1][2]

Common questions

What is the big dark beetle at my light?
In midsummer it may be a hermit flower beetle.[1][2]
Are the grubs killing my tree?
No; they feed only on wood that is already rotting.[1][2]
Is it dangerous?
No; adults are harmless.[2]

Sources

  1. University of Minnesota Extension, “Scarab beetles: hermit flower beetle and grape pelidnota (reviewed 2018).” extension.umn.edu/yard-and-garden-insects/scarab-beetles (accessed 2026-10-16)
  2. Iowa State University Extension and Outreach (Yard and Garden), “Hermit Flower Beetle (September 12, 2016).” yardandgarden.extension.iastate.edu/encyclopedia/hermit-flower-beetle (accessed 2026-10-16)
  3. iNaturalist, “Osmoderma eremicola taxon page (order and family).” www.inaturalist.org/taxa/226688 (accessed 2026-10-06)

Updated 2026-10-16. Built from sourced records. Spot an error? Tell us.