Spider Beetles

There are several species of Spider Beetle, all with the following common characteristics:

• Forewings hard and leathery, meeting along mid-line of dorsal surface
• Hindwings membranous, sometimes lacking
• Well developed thorax
• Biting mouth parts
• Complete metamorphosis with egg, larval, pupal, and adult stages

Members of the Ptinidae family have long antennae of 11 segments positioned between the eyes, plus a number of characteristics which give them a spider-like appearance:

• a stout body with hairy surface
• a waist-like constriction at the base of the prothorax
• 6 (not 8) long thin legs with 5-segmented tarsi

Distribution

The Australian Spider Beetle (Ptinus Tectus) originated in Australasia. It is a cosmopolitan species which reached Europe in the 19th century and is now widely distributed. It is rarely imported, and infestations often originate in birds' nests. There are 2-4 generations per year in unheated conditions. All stages, except eggs and young larvae, can over-winter.

The White-Marked Spider Beetle (Ptinus Fur) is a closely related species, which is also cosmopolitan in distribution.

The Golden Spider Beetle (Niptus Hololeucus) has similar feeding habits to the Australian species, exhibits a preference for moist places, and will occasionally infest textiles, especially if soiled with grease. It is increasingly common in domestic premises. There is usually one generation per year in unheated conditions in temperate lands, and peak activity is reached between August and November.

The Hump Spider Beetle (Gibbium Psylloides) is tolerant of cool conditions and can survive for long periods without food supplies

Significance

Spider Beetle larvae will infest all manner of dry animal and vegetable matter including grain, spices, fish meal, dog biscuits, dried fruit, and a wide variety of miscellaneous debris. They will scavenge among the debris of neglected stores, and have even been reported infesting insecticidal derris powder. The larvae bore holes in which to pupate, and in so doing may damage packaging or the commodities themselves. They also contaminate commodities with droppings and silk webbing.

Adult beetles will also damage packaging, including bags and sacks. Gregarious and nocturnal, they spend the day in cracks and crevices amongst packaging and the fabric of the store. Consequently they can thrive in old buildings where they find many harbourages.

Life Cycle

The female Australian Spider Beetle may produce 120 or more eggs over 3 to 4 weeks in early summer. They are laid either singly or in batches and, being sticky, will adhere to the substrate. At 20-25°C the eggs hatch in anything from 3 to 16 days, giving larvae which are fleshy, curved, covered with fine hairs, and relatively immobile, although they will rapidly curl up if disturbed.

Development takes at least 6 weeks, during which time the larvae moult 4 or 5 times. When mature, they wander in search of a pupation site, where they will spin a cocoon cell in which to pupate. These cocoons are often found on the outside of cartons through which the larvae have bored. Adults emerge after 20-30 days and will live for as long as 12 months. If disturbed, they will feign death. The full life cycle takes from 3 to 6 months depending upon the ambient conditions, and can take place in a temperature range of 5-28°C.

The life cycle of the Golden Spider Beetle resembles that of the Australian species. The eggs hatch in 11-30 days at 15-20°C, the larvae live for 150-250 days, and pupation takes 18-26 days, after which the adults live for up to 8 months.