Spider Beetles Decoded: From Identification to Behavior

Spider beetles are a curious group of insects that can pique your interest due to their distinctive appearance and behavior. With their long legs and oval or cylindrical bodies, they share a superficial resemblance to spiders, which gives them their common name 1. Ranging in size between 2 to 5 millimeters, these tiny beetles can vary in color from light brown to dark reddish-brown 2.

To better understand spider beetles, it helps to know some of their basic features and characteristics. They are typically found infesting stored products 1, and interestingly, they can be valuable in certain aspects to humans. For example, as predators, they help reduce populations of problem insects, especially caterpillars 3. With this knowledge, you’ll be better acquainted with these fascinating creatures, and you may appreciate their role in the complex world of insects.

Description and Appearance

General Characteristics

Spider beetles are small insects with a body size ranging between 2 to 5 mm long. These insects are oval or cylindrical in shape and have long legs and long antennae, which give them a superficial resemblance to spiders2. Their bodies are covered with hairs, and their colors can vary between species.

  • Size: 2 to 5 mm long
  • Shape: Oval or cylindrical
  • Legs: Long
  • Antennae: Long
  • Body: Covered with hairs
  • Color: Varies between species

Specific Species Attributes

There are multiple species of spider beetles, with each having distinct characteristics. The three most common species include the American spider beetle, the whitemarked spider beetle, and the smooth spider beetle.

American Spider Beetle (Mezium americanum)1:

  • Length: 1.5 to 3.5 mm
  • Body color: Dark reddish-brown to black, shiny
  • Legs, antennae, head, and thorax color: Pale yellow to cream hair

Whitemarked Spider Beetle4:

  • Length: 2 to 4.3 mm
  • Body color: Light brown
  • Markings: White markings on the body

Smooth Spider Beetle (Gibbium)5:

  • Length: Similar to the other species
  • Body color: Dark brown to black, smooth
  • Antennae: Shorter than the other species
Species Length (mm) Body Color Hair Color/Markings
American Spider Beetle 1.5 to 3.5 Dark reddish-brown Pale yellow/cream
Whitemarked Spider Beetle 2 to 4.3 Light brown White markings
Smooth Spider Beetle Similar Dark brown to black Smooth

In summary, spider beetles are small, oval-shaped insects with long legs and antennae, making them resemble spiders. There are several species with varying colors and hair coverage. Paying attention to these attributes can help you identify the specific species of spider beetle you encounter.

Habitat and Behavior

Living Environment

Spider beetles are adaptable insects that can infest various environments, such as homes, warehouses, mills, storage areas, and even museums. They can be found in areas like attics, pantries, and basements, where they seek moist and dark conditions to thrive. These beetles belong to the family Anobiidae or Ptinidae in North America, and they are often considered scavengers because of their feeding habits.

Feeding Habits

Some common food sources for spider beetles include:

  • Cereals
  • Flour
  • Grains
  • Dried fruits, like dates
  • Seeds, beans, and nuts, such as almonds
  • Chocolate powder
  • Pet food
  • Dead insects
  • Rodent droppings

As you can see, they have a diverse palate, which allows them to infest numerous places where these foods are stored or can be found.

Behavioral Traits

Spider beetles have some notable behavioral traits, which play a significant role in their life cycle:

  • Cocoons: They create cocoons for their eggs, choosing concealed spots that are moist and dark.
  • Moisture: They’re attracted to moisture, as it’s a vital component for the success of their eggs and larval development.
  • Scavenging: They are known as scavengers because they feed on a wide variety of materials, showing great adaptability in their diet.

By understanding the habitat and behavior of spider beetles, you can better monitor and manage their presence in your home or other environments. Remember to always keep an eye on potential infestation sources and maintain a clean, dry living space to minimize the chances of these bugs making themselves at home.

Spider Beetles and Humans

Infestation in Homes

Spider beetles can be a nuisance when they infest your home, especially in pantries, kitchens, and storage areas. These small brown beetles are scavengers, feeding off items found in your home. To prevent infestations, keep your living spaces clean and store food in sealed containers.

In case you spot a spider beetle infestation, you can use a vacuum cleaner to remove them from the affected areas. However, it’s essential to inspect your home thoroughly, as these pests have a habit of hiding.

Damage Caused

Aside from being a nuisance, spider beetles can cause damage to various items in your home. They are notorious for feeding on old wood, books, silk, wool, and stored food products. The damage can occur in the form of holes in packaging, as well as in grains and cereals, which can contaminate your stored food.

To minimize damage caused by spider beetles, be proactive in inspecting storage areas and keeping an eye out for signs of their presence. By doing so, you can take appropriate control measures before the infestation becomes extensive.

Prevention and Control

Prevention Strategies

To prevent spider beetles from infesting your home, you should focus on proper food storage and cleanliness. Store food items in airtight containers to keep pests out and maintain a clean environment. Sweep or vacuum food crumbs and spills regularly to deter beetle attraction. Additionally, seal crevices and cracks in your home to eliminate potential nesting sites for spider beetles.

Treatment Options

If you find yourself dealing with a spider beetle infestation, here are a few treatment strategies to help you get rid of these pests:

  • Vacuuming: Thoroughly vacuum any infested areas, especially cupboards or shelves holding infested items. Dispose of the vacuum bag outside of your home to prevent re-infestation.
  • Insecticides: While insecticide sprays are not generally recommended for spider beetles, you can consult a pest control professional for advice on whether an insecticide treatment would be appropriate for your specific situation.
  • Traps: If using traps, consult with a pest control professional to ensure they are properly set and used effectively.

Remember to check for infestations regularly and address them promptly before they become a larger issue. With proper prevention and treatment efforts, you can keep spider beetles and other pests at bay.


  1. https://hortnews.extension.iastate.edu/spider-beetle 2 3
  2. https://extension.psu.edu/spider-beetles 2
  3. https://www.si.edu/spotlight/buginfo/beetle
  4. Source
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  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

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