Whitemarked Spider Beetles

Facts, Identification & Control

Scientific Name

Ptinus fur

Appearance

The whitemarked spider beetle adult is about ¼ inch long and light brown in color with patches of white hairs on the front and back of the outer wings. Male specimens are smaller than females. This group of beetles is called spider beetles because adults look a bit like small spiders with long legs and an unusually large, globe-shaped abdomen. However, the shape of the whitemarked spider beetle’s abdomen is more elongated when compared with other members of the spider beetle group. The larval or grub stage is shaped like a C” and cream colored with a light brown head. Full-grown larvae are just about the same length as the adults and look somewhat like the larvae of the drugstore beetle.

Reproduction

Whitemarked spider beetles develop by complete metamorphosis and go through four stages: egg, larvae (grub) pupae (cocoon) and adult. Depending on temperature and humidity, it takes about four to nine months to complete one generation. Females lay individual eggs in cracks and crevices close to the beetle’s food supply. Generally, eggs hatch in about two to three weeks. Larvae go through three instars, taking about two to three months to complete the larval stage. The full-grown larvae spin a silk cocoon web and either go into an extended resting period or pupate immediately. The pupal stage takes about two to three weeks to complete, but adults may remain within the cocoon for a month or more before developing into sexual maturity. Upon emergence, adults feed and mate. Whitemarked spider beetle males, but not females, have the ability to fly. Adults may be seen on basement walls in the winter.

Behavior, Diet & Habits

Ptinus fur are scavengers that feed on damaged or spilled products and organic matter. Preferred foods include seeds, grain debris, herbs, dried fruit, almonds, beans, cocoa, cereals, chocolate powder, corn meal, dates, dried mushrooms, dried soup, animal skins, feathers, bat droppings and dead insects. They are often found in humid environments and feed on foodstuffs spoiled by dampness. Whitemarked spider beetles are not likely to infest products unless those products, however the beetles will infest damaged food containers and contaminate items with feces, pupal cases and parts of their bodies.

More Information

Infestations are found in warehouses, grain elevators, museums, libraries, homes and any structure where a suitable food source is found. Sometimes, the source of an infestation can be traced back to the beetle’s activity in birds’ nests in and around structures. In general, the most likely locations for whitemarked spider beetle infestations are homes and commercial food storage or production facilities.

Whitemarked spider beetle control, like other stored product pests, depends on sanitation, inspection and direct control actions. Managing this beetle is very difficult since it feeds on so many different items. For example, adult beetles found in the kitchen pantry may be originating from a bird or rodent nest, bat droppings in the attic space, or from dead insects in an exterior or interior wall.

Some important considerations and procedures for both homes and commercial warehouses are:

  • Remove spilled food daily and clean with a vacuum, especially along walls and edges of cabinets and food storage pallets where spider beetles and food products tend to accumulate.
  • If possible, humidity control equipment should be used to reduce inside moisture.
  • Use sticky traps to capture beetles. Your pest management professional will provide identification of insects on the traps. Place traps close to where the beetle’s sources of food are located.
  • Inspect food products you purchase at the store.
  • In a warehouse, inspect salvage areas where broken packages are kept prior to disposal and be sure to keep food storage pallets at least 18 inches from the walls. This makes cleaning and inspection much easier for your staff and your pest management professional.
  • Inspect the interior and exterior of your home or building for the presence of damaged grains and seeds, opened or damaged food containers, dead insects, bird and rodent nests.
  • Organize and rotate food items so that older products are used or shipped out before newer ones. This is important since whitemarked spider beetles move from infested products more and more as the infestation increases.
  • Store products in containers with tight fitting lids, especially if the contents are not used often. In the warehouse, put infested products inside sealed plastic bags before disposal. This will help lessen the spread of the beetles.
  • The use of cold and heat is effective to kill adults, larvae and eggs. Contact your pest management professional for advice and recommendations before using these methods yourself.
  • Contact your pest management professional for any assistance you need for conventional insect control using liquids, dust or fumigant insecticides. Control of whitemarked spider beetles is rarely a simple, straightforward task. Therefore, the advice, service and recommendations from your pest management professional are mandatory to ensure the work is done safely and effectively.