It’s an insect, it’s a stored product pest, it’s … spider beetle!

by Frank Meek

Of all the insects and arthropods that can be classified as a stored product pest, the spider beetle (Ptinidae, a subfamily of Anobiidae) is unique in appearance and diversity. This insect group is found throughout the world; and within the U.S. there are more than 50

species, with about a dozen classified as pests. They’re generally thought of as a minor stored product pest — until your client has an infestation.

Let’s start with the name:

A spider beetle looks more like a spider than a beetle. Like all insects, it has six legs, but the antennae give it the appearance of having two additional legs. Combine that with the spider-like shape — the head is hidden under the body, and it appears to have only two body regions like a spider. It even creates webbing like a spider, so the common name is fitting.

As a pest of stored products, preferred materials in which these insects can be found include:

• Broken grains
• Whole grains
• Seed
• Dried fruit
• Dried meats
• Fish meal
• Wool
• Hair
• Feathers
• Drugs
• Root material
• Rodent droppings
• Insect and other animal carcasses
• Plant and animal museum artifacts
• Bird and mammal droppings

Additionally, they can be found in the nest sites of bees, wasps, birds and mammals. They also tend to like wooden structures.
Most species are similar in size and reproductive potential, averaging between 1/16 and 1/8 in. The female produces less than 100 eggs during her life. The eggs hatch into larvae, which will go through three molts or instars before they leave the food source to pupate. The egg-to-egg time varies by species but is typically between three and nine months when there’s humidity and a food source. At least one species, the brown spider beetle (Ptinus clavipes), reproduces normally and parthenogenetically — an unfertilized egg developing into an individual.

Some members of this insect group remain alive and active at freezing temperatures; others require high humidity (70%) and temperatures in the 70 to 85°F range. Spider beetles aren’t just unusual; they’re versatile, adaptive and different.

You can reach Meek, international technical and training director for Orkin, at fmeek@rollins.com.