Solving the mystery of miniature brown beetles

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April 3, 2024

Stephostethus lardarius is one of many minute brown scavenger beetle species in Latridiidae. Photo: Henrik_L / iStock / Getty Images Plus / Getty Images

Stephostethus lardarius is one of many minute brown scavenger beetle species in Latridiidae. Photo: Henrik_L / iStock / Getty Images Plus / Getty Images

I start receiving identification requests and questions around this time of year involving small brown beetles. The setting and location may change from one request to the next, but the story is often similar: Tiny brown beetles suddenly appear in a client’s home or building with no clear indication of where they may be coming from.

In some cases, numbers can reach into the hundreds per day. The size of the beetle may align closely with some reinfesting wood-boring beetles, which lead to understandable concern and urgency for pest management professionals (PMPs) who don’t immediately recognize these tiny, but troublesome invaders.

There are millions of described beetle species on the planet, so you can’t immediately assume the culprit is always the same. But, in many cases, the miniature mystery beetles are one of several species in the family Latridiidae, commonly referred to as minute brown scavenger beetles, plaster beetles, or fungus beetles. Their common names are derived from their association with high-moisture conditions where they can find their primary food source: the hyphae and spores of mold and fungi.

While these beetles generally live outdoors, they can thrive indoors in damp wall voids or basements where high moisture and zero airflow allow mold, mildew and fungus to grow. Minute brown scavenger beetles are common in newer construction homes and commercial structures, where damp lumber and other materials get sealed up during the building process. But these species may also be found in agricultural and commercial settings where high-moisture conditions occur.

Dr. Michael Bentley, BCE

Dr. Michael Bentley, BCE

Minute brown scavenger beetles measure between 1.2 to 1.6 millimeters in length. Adults are generally reddish brown to light brown in color with punctate elytra, or tiny indented rows of holes on their wing covers. Body shape and the width of the pronotum can vary across species, with some having a thin elongated body and a narrow pronotum. Other species may have a shortened body and a wide pronotum that extends beyond the head.

Approach control of these beetles much like you would for stored product pests: Find and eliminate the food source. For minute brown scavenger beetles, this means locating and correcting the moisture problem that is sustaining the mold or mildew.

Resolving the problem quickly is key, as the moisture conditions and abundance of tasty beetles can attract other scavengers and create a secondary infestation.

About the Author

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Dr. Bentley is director of training and education for the National Pest Management Association. You can reach him at mbentley@pestworld.org.

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