By Chris Williams on September 4, 2018.

My wife wanted me to check for a plumbing leak in the guest bathroom upstairs. When I opened up the wall, it was full of something gross that looked like moldy dog food (we have a dog) and there were also what looked like tiny beetles in there. What could that be and how did it get there?

J. W., Grafton, MA

It could be exactly what you think it is – moldy dog food. Take a closer look. If it looks like the dry dog food that you feed your dog, then I would say that you either have, or have had, a mouse problem. While you’re at it, save some of those beetles for a positive identification from an expert.


Mice are known for hoarding or caching food away for a “rainy day.” They will collect bits of food, such as seeds (including birdseed), dry pet food, and anything else they can carry in their cheek pouches and will hide it in places like wall voids, behind a kick plate in the kitchen, under or inside appliances, in stuffed furniture, stove pan drawers, even in the void under the bathtub. Dry pet food is frequently hoarded because it is often available in a pet bowl 24/7 and extra is stored in a large bag in the garage or pantry (see Do Mice Eat Dry Pet Food?).

Mice generally don’t travel more than 30 feet from their nest to find food, but that 30 feet can be in any direction and they tend to hide caches of food within 10 feet of their nest (see Where Do Mice Nest?). Even though the cached food is upstairs, it was probably collected by a mouse in your kitchen or lower level (wherever you feed the dog or store its food) and carried up through wall voids to the upper floor. But there may be hoarded food in other places as well.

Shutterstock. Larder Beetle, one of the many “secondary pests” from mouse food stores

Most of this hidden food is never eaten by the mouse and instead gets old, and moldy, and eventually is infested by food beetles, moths, or mites that would normally be feeding on stored food in a kitchen.


Mouse food store of maple seed pods etc. Z. Ciras.

The fact that the food is moldy might confirm your suspected plumbing leak. The tiny beetles could be either a type of fungus beetle that has been feeding on the surface mold or one of the stored food beetles that scavenge on various foods and especially like foods that are older and damp. In either case, you have a secondary pest problem, whether or not you have a mouse problem. Either fungus beetles or food beetles could go on to infest other items in your home if conditions are right.

Don’t close your wall back up just yet. You are in need of the services of a pest control professional who will conduct a thorough inspection to determine exactly what is going on and what type of pest control services you need. Beetles or mice, our experienced and certified technicians can solve your problem. Give Colonial Pest a call today.

If you want to do a little sleuthing on your own, check out this Colonial blog: Telltale Signs That You Have Mice!

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