Spider beetles
Ptininae species

Order: Coleoptera
Family: Anobiidae
Acronym: PTI

Ecology

Spider beetles are a family of beetles that look somewhat like small spiders. The family contains about 450 species. In Canada, where the beetles are widely distributed, 20 species are estimated to occur. Both adult and larval spider beetles are scavengers and feed on materials of plant and animal origin. They have been known to feed on stored grain and moist animal skins. Spider beetles have been recorded in Canada in houses, flour mills, warehouses, stables, bakeries, mills, granaries, basements, wooden barns and grain elevators.

Damage

Spider beetles are generalist feeders and do not create any distinctive damage. Both adult and larval feeding causes damage to the commodity. They feed on stored wheat, cereal products, grain dust, spices, hay, bread, fish meal, decaying plant and animal refuse, wool articles, flour, animal feed, dried fruit and zoological collections. The adults and larvae chew irregular holes in grain kernels.

Several larvae will create a feeding cluster. The larvae secrete a substance and stick several grain kernels together to form a cluster in which they will feed.

Spider beetle infestations in flour may result in the accumulation of silk and granular materials in the flour which can be removed by sifting the flour. These materials may not be able to be removed from coarser milled products and therefore infested stock may have to be sold as feed. The presence of spider beetles is an indication of poor sanitation. Signs of infestation are contamination with silk, accumulation of granular materials, presence of adults and silk cocoons.

Life history

In all species, the adult is 2 – 4.5 mm long. It is globular in shape and the head is concealed when viewed from above. It has very long antennae and long legs. The adult in most species is brown in color. In many species, the adult is covered in hairs. In some species, the adult has white, gold or brown scales which form patterns on the elytra. In other species, the adult lacks hairs on the elytra and is very glossy. The thorax may be circular in shape and may be constricted.

The adult spider beetle may live for 3 or more months. The adult is nocturnal and active in dim light. It is capable of tolerating low temperatures. In some species, the adult can fly.

Breeding condition temperatures range from 10°C to 35°C. The female lays an average of 200 eggs. The female requires a free food and water source to produce the maximum number of eggs. She lays her eggs singly in the food source.

The larva is grub-like and C-shaped. It is white and robust. The larva is about 3 to 5 mm long. They have a well developed head and thoracic legs. The optimum temperature range for development is 20°C to 30°C. In general, spider beetles require high temperatures and high humidity for development. The larva usually moults 3 times. Under adverse conditions, it will moult even more. The range of development time is 60 to 350 days. Depending on the species, the mature larva will either spin a cocoon in which to pupate or it will form a pupa in debris.

Control

Controlling insect infestations

Images

Adult Spider beetle - Niptus holoeucus

Adult Spider beetle - Ptinus fur