Thank you for your question. I have forwarded your question to our entomologist. This was his response:

The offending insect is a smooth spider beetle, Gibbium aequinoctiale, named because the long legs and antennae, underslung head, and overall small size makes them resemble small spiders, but they really have no actual connection with spiders. They’re hardy little scavengers, and can subsist on almost any kind of organic matter – including food made of plant matter (e.g., grains, beans, pollen, etc.), animal matter (e.g., leather, carrion, etc.), fungi (e.g., mold, etc.), or a mix. In general, the best way to get rid of them is to figure out what they’re feeding on and clear out their food source. Likely sources are old packages of food in the pantry, bags of pet food, or musty basements or crawlspaces that favor fungus growth. They’re especially likely to target foods that have been exposed to moisture or that are stored in humid areas. They can’t fly, but they may wander on foot in search of new food sources; I’d hunt for food sources close to where you’re finding them, then move your search outward if you cannot find anything. If you find something with tiny round exit holes just big enough for the beetles to squeeze out of or with tiny, cream or beige-colored grubs or the silk cocoons they produce in it, then you’ve found their food source.

Being in a bathroom, I’d check for areas that may not dry properly or may have leaks that could be attracting them by producing molds. That may include under/behind sinks, toilets, showers, and bathtubs, or in the exhaust fan or vents.

If you cannot find the source, then they can typically be eliminated by applying a residual insecticide to the areas where they are turning up. However, I would interpret their presence as a hint of a potential moisture or sanitation issue that could have greater consequences than the beetles do, and prioritize finding and correcting whatever allowed them to become a problem in the first place. The beetles themselves are harmless, but can become a nuisance when they keep appearing.

If you have any other questions or concerns, please contact:

Jamie Kopco PhD BCE
Pesticide Education Program
The Pennsylvania State University
209 Special Services Building
University Park, PA 16802
Email: <personal data hidden>
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