Dermestid beetles are scavengers that feed on a variety of household materials derived from plant or animal matter. There are several genera and at least 39 species of dermestid beetle inhabiting Colorado. About six species are reported in homes and buildings. Those most encountered in the household include certain Anthrenus spp., some Dermestes spp., and the warehouse beetle (Trogoderma variabile). It is important to note that the larvae of dermestid beetles resemble certain species of small millipedes (Polyxenus spp.). Unlike dermestid beetles, these millipedes do not damage household materials.
This genus comprises the smallest dermestid beetles found in homes, with the most common being the black carpet beetle (Attagenus unicolor). Other species occurring in Colorado homes include the varied carpet beetle (Anthrenss verbasci), furniture carpet beetle (Anthrenus flavipes), and Anthrenus scrophulariae. Measuring approximately 2-5 mm long (1/20-1/5 inch), adults of the black carpet beetle are round and have a dark body with brown legs. Larvae are brown and 12 mm (0.5 inches) long with a spiny body that narrows near the head and often has a small tuft of hairs at the tip. The larvae of this genus feed on plant and animal matter, and commonly inhabit abandoned bee and wasp nests. As larvae develop, homeowners may observe the accumulation of larval skins since they generally do not feed over a wide area. Adults are strong fliers and typically enter buildings in spring and colonize areas where dead insects collect behind walls or in attics.
Trogoderma spp. are often a pest of stored foods since they develop on plant materials like seeds, nuts, herbs, spices, and cocoa. Adults have oblong bodies and are about 3-4 mm long (1/10-1/6 inch). They are generally dark bodied, but some species such as the warehouse beetle (Trogoderma variabile) have wavy bands or faint patches on the wing covers. Larvae of Trogoderma spp. have elongated bodies that are lighter colored than many other dermestid species.
Beetles in this genus typically feed on meat-based material such as dried pet foods. The beetles are oblong and about 6-10 mm (1/4-1/3 inch) long. The larder beetle (Dermestes lardarius) has a yellow band with dark spots on the wing covers, while most beetles of Dermestes spp. are dark colored. The reddish-brown larvae have tapered bodies and leave the food source when fully grown to produce a pupation chamber. The mature larvae have strong mandibles and excavate wood beams for pupating. Some Dermestes spp. are used by museums and taxidermists to remove flesh from bones.
- The larvae of dermestid beetles are typically hairy, elongated, dark-colored, and have clubbed antennae. Some larvae have spines located on the back of the abdomen. It is worth noting that Polyxenus spp. are millipedes frequently misidentified as dermestid beetle larvae due to their appearance.
- Dermestid beetles are a commonly encountered pest in households and buildings. The larvae of some species feed on plant matter including stored grains or seeds, nuts, herbs, spices, and cocoa. Most scavenge on materials of animal origin such as dead insects, pet hair, lint, wool, furs, and feathers.
- Preventative measures include vacuuming lint and hair regularly, removing dead insects from windowsills, storing susceptible materials below 40°F, and sealing the edges of windows, doors, vents, and openings under eaves to prevent beetles from starting a new infestation. When treating with insecticides, it is also important to identify and remove potential breeding sites.
Adult and larva of dermestid beetle. Image credit: Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org
These small millipedes (Polyxenus spp.) are commonly misidentified as dermestid beetle larvae. They have pale brown bodies that measure 1 mm in length, making them smaller than the larvae of dermestid beetles. When indoors, the millipedes tend to aggregate around areas with high moisture such as kitchen sinks and bathrooms. While their sudden appearance may be alarming, these millipedes do not harm household materials. Image credit: Joseph Berger, Bugwood.org
Adult (top) and larva (bottom) of black carpet beetle. Image credit: Clemson University – USDA Cooperative Extension Slide Series , Bugwood.org
Larvae of warehouse beetle. Note the light color in comparison with other dermestid larvae. Image credit: Pest and Diseases Image Library, Bugwood.org
Male (left) and female (right) warehouse beetles. Image credit: Pest and Diseases Image Library , Bugwood.org
Reddish-brown larva of larder beetle. Image credit: Mohammed El Damir, Bugwood.org
Larder beetle. Note the thick yellow band with black spots on the elytra (wing casings). Image credit: Joseph Berger, Bugwood.org
Insect collection infested with dermestid beetles. Much of the collection has been consumed. Image credit: Rebekah D. Wallace, University of Georgia, Bugwood.org
Life history and habits
All beetles have four life stages: egg, larva, pupa, and adult. Some species of dermestid beetle take two years to develop, while others complete development in six weeks.
One generation of Attagenus spp. is produced annually, and adults can lay up to 90 eggs at a time. Species in this genus overwinter as a pupa or late-stage larva. Trogoderma spp. develop continuously and can produce more than one generation annually. Dermestes spp. typically overwinter as adults, and the beetles are strong flyers commonly seen in late spring and early summer. The larder beetle can lay up to 135 eggs.
Sealing the edges of windows or doors, vents, and openings under eaves will help prevent beetles from entering the building and starting a new infestation. Storing clean materials in insect-proof containers can help prevent infestations. When possible, susceptible materials can be stored at temperatures below 40°F to prevent development of dermestid beetles. Vacuuming lint and hair, removing collections of dead insects around windows, and cleaning any spilled grains will reduce the availability of suitable breeding sites for dermestid beetles. Pay extra attention to clean areas where lint accumulates and the seams of furniture where food crumbs collect. Vacuumed material should be disposed of immediately.
The presence of discarded larval skins and live larvae are indications of an infestation and can help identify the breeding site. Adults are more mobile than larvae and can be found far away from breeding sites. For dermestid beetles that develop on animal material, inspect areas where lint and hair accumulate such as under carpets and along carpet edges, under furniture, in floor cracks, in registers and ducts, and in the folds of upholstered furniture. Dermestid beetles can also be found breeding on items made of fur, hair, feathers, or preserved animals, and on woolen clothing and yarn stored in attics, basements, and closets. Less obvious breeding sites include old animal nests attached to the building, and collections of dead insects behind walls or around windows.
Dermestid beetles that develop on plant material can be found on flour, grains, nuts, and seeds. It is important to pay extra attention to areas containing these food products such as the pantry. Dermestid beetles can also develop in the nesting areas of rodents and squirrels where nuts are stored.
The most reliable technique for addressing dermestid beetle infestations is to locate and remove infested objects. Objects that cannot be removed or destroyed, such as woolen items or minimally infested food, should be frozen or heat treated to kill all life stages. When an infested item can be frozen, place it in a deep freezer below 0°F for three days or more. Heat treating at temperatures above 130°F for several hours will kill the insects. Clothes driers and dry-cleaning will kill insects infesting fabric or clothing. It is important to note that large items will require longer freezing or heating times to penetrate the material and kill the insects.
When insecticides are used for treating dermestid beetle infestation, it is important to also conduct a thorough cleanout of potential breeding sites and removing any existing insects. Insecticide applications alone are not an effective management approach. However, they can provide some control when used as a supplement to other control methods. For more information, refer to the chemical control section on the CSU dermestid beetle factsheet.
Hodgson, E., Coates K, and Roa A. 2008. Dermestids. Utah State University – Extension. Available https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1891&context=extension_curall
Utah State University (n.d.). Carpet Beetles. Utah State University – Extension. Available https://extension.usu.edu/pests/schoolipm/structural-pest-id-guide/carpet-beetles