**Hairy Fungus Beetles** (*Mycetophagus* spp.) are small beetles that are often considered nuisance pests when they invade homes, typically during the fall and winter. They are harmless scavengers whose sole diet is various types of fungi, yeasts, and molds. Their presence indoors is a clear indicator of a **chronic moisture problem** that is supporting fungal growth, such as moldy wood, mildewed materials, or damp stored foods. They are not known to damage wood or fabrics directly.
Taxonomy and Classification
Hairy Fungus Beetles belong to the order Coleoptera (beetles), family Mycetophagidae (fungus beetles). They undergo complete metamorphosis. Like all fungus beetles, they are highly specialized to consume the fruiting bodies and mycelia of various fungi, acting as natural recyclers in forests. They only become structural pests when human structures create the perfect, damp, moldy environment for their food source.
Physical Description
Adult Hairy Fungus Beetles are small, 1/8 to 1/4 inch long.
- **Appearance:** Oval-shaped and often dark brown or black, with a coating of fine, yellowish-brown hairs (**hairy**), giving them a fuzzy appearance. Some species have reddish-brown markings.
- **Larvae:** Creamy white, cylindrical larvae, also found feeding in the moldy material.
- **Location:** Found crawling near areas of high moisture, such as leaky plumbing, damp crawl spaces, basements, wall voids with mold growth, or around stored food that has become damp and molded.
- **Behavior:** They are primarily nocturnal and will scatter quickly when disturbed.
Distribution and Habitat
Hairy Fungus Beetles are widely distributed. Their natural habitat is rotting logs, tree stumps, and under bark, where they feed on wood-rotting fungi. Their indoor habitat is any structurally damp area—leaky pipes, poorly vented crawl spaces, wet insulation, or stored goods that have mildewed.
Behavior and Conflict
The beetles are benign, but their presence indicates a more serious underlying problem.
- **Indicator Species (Key Conflict):** Their appearance indoors is a warning sign that there is an excessive and chronic moisture and mold problem within the structure that requires professional attention.
- **Nuisance:** They are primarily nuisance pests, crawling on walls, floors, and windowsills, often in large numbers if the moisture source is severe.
- **No Direct Damage:** They do not feed on dry wood, sound materials, or healthy stored foods; they only consume the mold and fungi growing on those materials.
Management and Prevention
Control is achieved by locating and eliminating the moisture source, which eliminates their food source.
- **Moisture Control (Crucial):** Identify and repair all leaks (plumbing, roof, foundation). Use dehumidifiers and improve ventilation in basements and crawl spaces to maintain humidity below $60$ percent.
- **Sanitation:** Remove and discard all moldy, wet materials (food, paper, cardboard, wood) where the beetles are living.
- **Cleanup:** Thoroughly dry the affected area and use an appropriate fungicidal cleaner to remove the mold growth.
- **Pesticides:** Chemical treatment is generally not recommended or necessary. If large populations persist after moisture control, a residual insecticide can be applied to cracks and crevices, but this is always secondary to fixing the water leak.
Conservation and Research
Hairy Fungus Beetles are managed as indicator organisms. Research focuses on their role in forest decomposition and using their presence as a cheap, non-toxic way to survey for hidden moisture problems in historic buildings.