Fungus beetles is a general term covering several different beetles associated with damp, humid conditions where fungi, molds, and mildew occur. When new homes are built, moist uncured lumber and/or freshly plastered or papered walls that become covered with molds attract these beetles. Some occur in sawdust left in wall voids after construction. They often build heavy populations throughout late summer and early fall. These mold-feeding beetles sometimes are found in decaying plant material, woodpiles, mammal, ant, or termite nests, damp cereals, grains, herbs, spices, cheese, jam, jellies, fibers, and carpeting, especially in cellars. Attracted by lights, these small beetles can crawl or fly through window or door screens and then wander aimlessly. Heavy populations may first show up trapped in bathtubs and sinks, or around lamps and TV sets. They are simply a nuisance by their presence and do not bite, sting, spread human diseases nor damage wood, food, fabric, etc.
|Common Name||Scientific Name|
|Foreign Grain Beetle||Ahasverus advena (Waltl)|
|Hairy Fungus Beetle||Mycetophagus punctatus Say|
|Plaster or Minute Brown Scavenger Beetle||Melanophthalma americana Mannerheim|
|Sigmoid Fungus Beetle||Cryptophagus varus Woodroffe & Coombs|
|Acute-angled Fungus Beetle||Cryptophagus acutangulus Gyllenhal|
The foreign grain beetle is camel-brown colored and about 1⁄16-inch long with a conspicuous rounded lobe or "knob" on the four corners of the thorax (area between the head and wing covers). The body is covered with dense pubescence (short, fine hairs) and dimple-like punctures with a clubbed antennae. Other fungus beetles are less than 1⁄12-inch long with body color varying from yellowish to black. Also, most have punctures on the body and clubbed antennae. A good quality hand lens or microscope is necessary to see these characteristics.
Life Cycle and Habits
Most complaints of these nuisance beetles occur in late July, August, and September. Beetles often become quite abundant, especially after a period of rainy weather. However, development from egg to adult depends on temperature. Some beetles complete their life cycle in 25 to 36 days at 75°F, in 54 days at 65°F, or up to five months and longer at lower temperatures. Beetles are attracted to lights and feed entirely on the spores and hyphae of fungi. Later, eggs are laid on food material such as poorly seasoned green lumber, wet plaster and wall board, moldy grains, etc. Larvae develop in the molds, maturing to adults later. Sometimes, stored foods may become contaminated from cast skins and excreta. Also, infestations are associated with poor ventilation, high humidity, plumbing leaks, etc.
Most infestations are temporary and self-limiting, but their presence is objectionable to many homeowners.
Often it is difficult to locate the source of infestation since beetles may be feeding on fungi associated with neglected grains, yeast, moldy flowers, wall voids with rodent and insect nests, decaying plant materials, moldy wallpaper, freshly plastered walls, around moist window cases, or poor plumbing. Any action taken to dry out damp conditions supporting fungal growth, essential to these beetles, will greatly reduce or eliminate populations. Most homes dry out naturally within a year or two, and the fungi disappears along with the beetles. Usually adequate artificial heating and ventilation will stop infestations. Periods of dry weather with relatively low humidity (below 60 percent) will reduce numbers. Be sure that dry foods are stored in insect-proof containers (glass, heavy plastic, or metal) ideally with screw-type lids free of mold. A strong suction vacuum cleaner with proper attachments will collect many beetles.
If moisture problems cannot be corrected, commercial household labeled fungicides may be effective in eliminating or reducing fungal growth in selected areas. Household aerosol sprays of pyrethroid insecticides (these usually end in "–thrin") will kill many beetles when applied in crevices under baseboards, and around windows, doors, and lights. Total release aerosol insecticides (commonly called bug-bombs) are usually ineffective in controlling these pests as the fumes rarely reach all the voids where the beetles may be developing. If cleaning and reducing fungal growth does not eliminate these pests, seek the assistance of a pest control professional who has dusts and other products that are registered for application into wall voids and other hard to reach places. Before using any insecticide, always READ THE LABEL and follow directions and safety precautions.
This publication may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to constantly changing labels and product registration, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author, The Ohio State University, and Ohio State University Extension assume no liability resulting from the use of these recommendations.