There are several pest beetles in the beetle family Lathridiidae that feed on the hyphae and spores of molds, mildews, and fungi. The family is known as the "minute brown scavenger beetles," but they are usually called mold or plaster beetles, or sometimes fungus beetles. Most are found worldwide. Note that there are other beetle families that also contain tiny fungus-feeding beetles.
The mold or plaster beetles are some of the tiniest insects that you will deal with at only 1/32 to 1/8-inch (0.8-3 mm). They are reddish-brown to dark brown in color. The head and pronotum are narrowed and the wing covers have parallel rows of pits. Antennae are 8 to 11 segmented with 1-3 segment club. A few species can fly and are attracted to light. Larvae are elongated, white to pale yellow.
Outside, these beetles are found in damp leaves, under bark or decaying roof shakes, and similar sites. The plaster beetle got its name when plastered walls were more common in homes and beetles were found feeding on mold growing on the still damp plaster.
The Mold/Plaster Beetles as Pests
These beetles commonly show up in buildings that have a moisture issue, either because of damp building materials in new construction, or plumbing or roof leaks, high humidity or condensation problems. They can be pests in new construction where still "green" lumber, damp sheetrock or wallpaper, wet plaster, or other materials are slow to cure or dry and fungi can grow on the surface. They can also infest stored food products that are damp and growing mold and can become problems in food-processing plants.
Mold or plaster beetles become problems mainly in periods of extended wet weather and in hot, humid summer months. Both larvae and adults feed on mold and can build up to high numbers in cellars, wall voids or other damp enclosed spaces. They may be first seen in months after construction when emerging adults appear. As with other moisture pests, control involves drying out the damp site that is growing mold using fans dehumidifiers, or heat. The beetles and the mold require humidity above 20%. Use a moisture meter to find damp areas. In new construction, and especially in humid weather, it can take many months for building materials to dry completely. Insecticide treatment may be needed in the meantime. Vacuuming can remove emerging adults.
Key Points to Remember - Mold and plaster beetles are tiny nuisance pests where moisture problems allow mold to grow. The beetles do not damage materials since they are feeding strictly on the surface mold. They can sometimes become pests in warehouses and facilities with damp conditions, causing contamination problems.