The beetles are fairly small, measuring 1.5 to 4mm in length. The body is strongly convex, rather like the ladybird beetle and is characterised by the pattern of yellow, black and whitish scales on the body.
Between 20 and 100 eggs are laid by the female during spring and early summer on furs, woollens and any dried materials of animal origin.
When the larvae hatch out, they are hairy and brown with three bunches of golden hairs on the abdomen. They normally reach a length of 4-5mm. They tend to avoid the light and when disturbed, curl up into a ball.
The eggs hatch between 10 to 35 days depending on the temperature. The larvae can last at least a year depending on the quality of the food supply. The adult beetle lives from 7-41 days.
The adults appear in April, May and June and their resulting larvae hibernate during the following winter, pupating during the latter part of February and March.
On emergence the adult beetles seek the light so they usually fly to the windows. They fly to light coloured flowers where they feed on nectar and pollen. After mating, the females enter houses during late summer and autumn and lay their eggs in birds nests in roof voids and other suitable places. The larvae feed on feathers and wool soiled with excrement, dead fledglings etc.
Infestations of these insects mostly originate in birds' nests such as those of house-sparrow, house-martin, swift and starling. The carpet beetle larvae live on the soiled wool and feathers in the nest-lining and then manage to get under the eaves in the roof space. From here they crawl into the upper rooms of the house, usually following the hot water pipe system. They appear to be attracted to warmer situations. Airing cupboards often harbour substantial infestations. Carpet beetles do, however, sometimes fly through open windows and presumably initiate infestations directly, but infestations arising from birds' nest cause continual invasions. The first rule of control therefore is to remove birds' nests from eaves and all similar situations. If dead birds or rodents are found in chimneys or under floors they should be removed. Any pieces of old carpet or similar material in lofts or roof voids must be destroyed otherwise they will act as reservoirs of infestation.
The fully grown larvae of carpet beetles appear to be resistant to modern contact insecticides because they are able to crawl about long after they have come into contact with a lethal dose of insecticide.