It usually enters houses through open or badly fitting windows. The freshly hatched beetle is brown at first, and then turns black with light stripes on its wing cases. The females lay 150 to 200 sticky eggs in the food. The hatched larvae are the familiar mealworms, with a length of up to 28 mm. It may take a year and a half before the mealworms turn into beetles.
Massive infestation is therefore fortunately rare.
The adult beetles live for about 4 to 6 weeks. Drugstore beetles and mealworms not only eat any pastry and bakery products, they also soil them as well. The flour turns lumpy and smells mouldy. They prefer leftover wheat and flour waste. The drugstore beetle's larvae can bore passages or cavities in rotten wood or insulating materials, with the aim of finding a suitable place to pupate.