Spider Beetle

Spider beetles have globular bodies, which makes them look like spiders. 

Summary

Spider beetles are insects in the family Ptinidae. Their common name refers to the unique appearance of the beetles. Ptinids have large, rounded abdomens, making them look similar to small spiders. They are scavengers usually found indoors, living in pantries, warehouses, museums, and food processing facilities. However, they’re not numerous enough to be considered pests unless the conditions are right for their proliferation. 

Spider Beetles Species, Types, and Scientific Name

Spider beetles belong to the family Ptinidae, the same family as the death watch beetles (subfamily Anobiidae). They belong to the sub-family Ptininae, with approximately 600 species grouped into 70 genera. 

Many other prominent members of the same family are pests of stored food products. Examples of insects closely related to the spider beetles include the drugstore beetle (Stegobium paniceus) and Cigarette beetles (Lasioderma serricornis). In addition to being members of the same family, these insects also have a similar appearance, with a humped body and a head directed downwards. 

The common name is a reference to their appearance, which looks a lot like an arachnid at first glance. They have a rounded abdomen and a tiny thorax. Their heads are also hidden, especially when observed from above, just like a spider’s. Some of the most popular species include 

1. Australian spider beetles
2. Brown spider beetles
3. Golden spider beetles
4. White marked spider beetles

Appearance: How to Identify Spider Beetles

Spider beetles are small to moderately sized. Although different species vary in size, they’re typically about 2 – 4 mm (1/16 – 1/8 inch) long. As their name suggests, these beetles look a lot like tiny spiders. Their most conspicuous feature is their globular body. Their head is pointed downwards and is concealed under their body when you view them from above. 

Unlike actual spiders, ptinids beetles have six legs which is typical of all insects. However, the antennae on their heads often look like an extra pair of legs. This further contributes to their spider-like appearance. 

Most species are brown to reddish brown. They often have a smooth carapace, but some species have their bodies covered with fine hairs. Some species also have distinctive markings. Because of the globular shape of their abdomen and reddish-brown color, spider beetles may also be mistaken for bed bugs. Their C-shaped larvae are dirty white, and they have well-developed legs.

The small size of spider beetles and their reclusive nature make it difficult to discover an infestation. Most times, an infestation would have been underway for a long time before people detected them. The most obvious sign of an infestation is the sighting of a pupal cocoon or an adult spider beetle.

Habitat: Where to Find Spider Beetles

They are found in various locations all over the world. In every location where human civilizations exist, these beetles can survive there. In places where they’re found, they have a largely cosmopolitan distribution.

Ptinids are scavengers mostly found in association with stored food products. They can infiltrate food production facilities, warehouses, grain storage units, mills, and museums. They may also find their way into homes in pantries, food storage cupboards, and attics with insect, bird, or rodent nests. 

Spider beetles are attracted to moist areas. Hence, they’re typically more common during rainy periods. They are shy insects, and they stay hidden most of the time. They usually hide inside walls, within cracks of wooden floorboards, and in other locations where they can remain hidden from the light until it’s night-time. 

Diet: What Do Spider Beetles Eat?

They are scavengers. As such, they’re not picky about their diet. As indoor pests of stored products, they mostly consume grains. However, they can eat a variety of other foodstuffs such as seeds, almonds, rye bread, wool, flour, and dried mushrooms. In addition, they can feed on other non-food products such as animal skins, wool, silk, and books.

What Eats Spider Beetles? 

Spider beetles don’t have any notable defense mechanism against predators. Hence, they often get eaten by spiders,  lizards, birds, rodents, and other insectivorous insects in the home. 

Prevention: How to Get Rid of Spider Beetles

Because of the diverse nature of their diet, it can be difficult to prevent an infestation. They infest stored food products, so keeping your grains and other food products in airtight containers will help reduce the chances of an infestation. Regular cleaning and prompt removal of any rodent or bird nest inside your building will also help prevent infestation. 

If you suspect you have spider beetles in your space already, eliminating them is heavily reliant on your ability to identify the original source of the infestation. Unfortunately, this can be difficult considering the beetle’s varied diet and elusive nature. For instance, even though you may find them in your pantry, the real source of infestation might be somewhere within your wooden walls or in your attic. 

If you’re having difficulty locating the source of an infestation, place sticky traps in different parts of your home, especially in areas where the beetles have been spotted. Move the traps around as you capture more beetles until you locate the infested material and remove it. In case of a large infestation, it is always best to call a professional pest control company.

Related Animals

• Golden Tortoise Beetle
• Jewel Beetle 
• Hobo Spider

1. Wikipedia, Available here: https://en.wikipedia.org/wiki/Spider_beetle
2. Penn State Extension, Available here: https://extension.psu.edu/spider-beetles
3. Ehrlich / Ashley Smith, Available here: https://www.jcehrlich.com/blog/5-facts-about-spider-beetles/