An adult biscuit beetle © Siga (CC BY-SA 3.0) via Wikimedia Commons.

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Bread, or biscuit beetle (Stegobium paniceum) identification guide

The bread beetle, Stegobium paniceum, also known as the biscuit beetle or the drugstore beetle, is one of the commonest pest insects of stored food. It is able to feed on a variety of plant and animal products including bread and flour and even hot spices and drugs.

However, this beetle is not harmful to health and despite its close resemblance to the common furniture beetle (woodworm), it does not feed on wood.

Identification

The adult beetles are usually noticed first. They are small, between 2-4 mm in length, reddish-brown and, under magnification, reveal fine grooves running lengthways along the wing cases. Furniture beetles (or woodworms) are similar but are somewhat larger and darker and their antennae are shorter than the legs (in bread beetles the lengths are similar).

There are three flattened segments at the tip of antennae. The head is mostly hidden by the upper part of the beetle's thorax (the middle section of the insect). Biscuit beetles have large dark eyes.

The bread, or biscuit beetle, showing its body from above, the side and underneath — The adult bread, or biscuit beetle. Notice how the beetle's head is mostly hidden under the top of its thorax (the middle body section). The adult beetle has a body length of 2-3 mm. © Siga (CC BY-SA 3.0) via Wikimedia Commons. Composite of three images.

The grub-like larva of a biscuit beetle compared with a line drawing of the same — The grub-larva of a biscuit beetle and a line drawing showing its general characteristics. Larvae are similar to many other beetle grubs. Their maximum size is 5mm.

Distribution and habitat

The biscuit beetle is common across the world. It occurs in houses, stores, warehouses and kitchens throughout central and northern Europe, including the UK, sometimes in very large numbers.

Life cycle

In common with other beetles, this species passes through four life-stages: egg, larva, pupa and adult. The speed of development through the life cycle depends on temperature, moisture, quality and abundance of food. In cool temperatures (below 15ºC) there is only one generation per year, in moderate temperatures two generations, while at higher temperatures (above 23ºC) there may be five or more.

Eggs are laid by mated females on or near the foodstuff. When the larva emerges from the egg, it is less than 1mm in length. In its search for food, it may bite into packaged or hidden food sources. The larva increases in size and, at about 5mm in length, it enters the pupal stage. Before emergence as an adult beetle, a minimum of nine days is spent as the pupa in an oval shaped cell that is moulded by the larva using the food material.

Damage and control

Because bread beetle larvae thrive in dark, warm, undisturbed places, it is essential to search thoroughly for the food-source of the larvae if adults are found wandering around. Rarely-used dried-foods such as flour or spices are often the source of an infestation. Removing disused and old foodstuff should eliminate an infestation.

Adult beetles may be seen around fire-places and air vents with no apparent food-source available. These are likely to have come from nests of wasps or birds in the attic. Beware also of bread in fire-places that has been dropped down the chimney by birds. With suitable hygiene, and by preventing access into the attic by nest-builders, the successful eradication of this pest should be assured.