Hi Becky,

Thanks for contacting Ask Extension. You said the brown spots on your ceiling have been appearing for the past 6 months and the spots aren’t from grease splatters, etc since they are not over cooking or food prep areas. I can’t confirm without testing a sample but from looking at your pictures it could maybe be insect frass or feces. If we had an actual sample that we could look at under a microscope or do a substance analysis of, then it would be much easier to identify what this substance is and where it came from. There are lots of insects that enter homes in the fall, so I’m concerned that the spots have been appearing since spring and have continued through summer and into fall.

Various insects leave behind frass with an appearance that is unique to the insect. This allows you to determine what kind of insect infestation is taking place on the site. Some insects produce liquid frass, while others produce small, dry feces that are easy to catch. There is the possibility that the substance on your ceiling is insect frass but I can’t confirm this without a sample.

Insect frass is a visible sign of an infestation, but there are different types of frass. They can appear similar to the untrained eye, but there are significant differences. The insect may also have a unique method of disposing of frass, and this can also help the pest-control professional to correctly identify the insect. I’m assuming that you regularly have been cleaning these spots but they just keep coming back so I am recommending that you contact a pest control company so they can investigate and find the source for the spots. I am attaching a fact sheet on Integrated Pest Management for the Home that gives advice for preventing insects in the home. This fact sheet is designed to help get you started with an understanding of insects, weeds, and other pests in and around your home.

I hope this helps and that you find the source and solution for getting rid of these mystery spots.

Take care,
Jeffco Master Gardener Clinician Nancy