Spider Beetle Life Cycle: A Closer Look at These Intriguing Insects

Spider beetles are fascinating creatures that often go unnoticed in the world of insects. They thrive in various environments, and their unique life cycle sets them apart from other beetles. Understanding the spider beetle life cycle can provide valuable insights into their behavior and ecological roles.

The life cycle of spider beetles consists of several stages, starting from the egg and developing into a full-grown adult. During this process, you’ll notice that both the adult and the grub-like larval stage are scavengers. They feed on a variety of materials, such as broken grain, seeds, dried fruits, and even wool and feathers source.

As a curious observer, gaining knowledge of the spider beetle life cycle gives you a greater appreciation for these small yet complex insects. Keep an eye out for them as you explore various habitats and environments; you might be surprised at how much you can learn from them.

Spider Beetle Overview

Spider beetles are fascinating insects belonging to the family Ptinidae. You might mistake them for spiders initially, but they are actually part of the beetle order, Coleoptera. There are several genera of spider beetles, including Mezium and Gibbium psylloides, and they can be found across the world.

These beetles often have long, slender legs and antennae, giving them their name due to their superficial resemblance with spiders. Their body size generally ranges from 2 to 5 millimeters, with colors varying from light brown to dark reddish-brown.

Some notable features of spider beetles include:

  • Oval or cylindrical bodies
  • Long, skinny legs
  • Antennae covered in pale yellow to cream-colored hairs
  • Diverse species within the Ptinidae family
  • Presence in various habitats worldwide

Spider beetles undergo a lifecycle that consists of eggs, larval stage, pupal stage, and adulthood. Both adult and larval spider beetles are scavengers, feeding on a variety of organic materials.

In comparison to other beetles, spider beetles are relatively less known, but their unique appearance and diverse species make them an interesting study focus for enthusiasts and researchers alike. So next time you encounter a spider beetle, take a moment to appreciate the small details that make them distinctive members of the beetle world.

Identifying Spider Beetles


Spider beetles have a unique appearance, with their oval or cylindrical body shape and long, thin legs. Their color can vary between different shades of brown, black, yellow, and gold. They may resemble spiders due to their long legs and round bodies.


Spider beetles are usually quite small, ranging from 2 to 5 millimeters in length. These tiny insects may be hard to spot with the naked eye, but their distinctive appearance can help you identify them.

Comparative Description

When comparing spider beetles to other insects, you might notice some similarities with spiders such as their long legs and a similar body shape. However, spider beetles have six legs as opposed to the eight legs of spiders.

Distinct Characteristics

Some of the unique features of spider beetles include:

  • Cylindrical or oval-shaped body
  • Elytra (hardened wing covers) that may be shiny or dull
  • Long, thin legs that give them a spider-like appearance
  • Various color patterns, such as reddish-brown, black, yellow, or gold


Spider beetles have a cosmopolitan distribution and can be found across North America, Australia, and other parts of the world. They are known to infest stored products, warehouses, museums, homes, and other environments where food storage is present.

Prominent Species

The American spider beetle (Mezium americanum) is a common species of spider beetle found in North America. They are reddish-brown to black in color, with a shiny, globular abdomen, and can be recognized by their pale yellow to cream-colored hairs covering their head, thorax, legs, and antennae.


You can find spider beetles in various environments, typically where food storage occurs. They tend to dwell in cracks, shelves, and storage areas in homes, warehouses, or museums. Keep an eye out for these insects in places with stored products, as they are known to infest such areas.

Spider Beetle Life Cycle


Spider beetles begin their life cycle as tiny eggs. Females of some species cover their eggs with materials like remnants of their meal to protect them. The eggs typically take around 7 to 10 days to hatch.

Larval Stage

After hatching, the spider beetles enter their larval stage. During this stage, they appear as white or pale yellowish grub-like creatures. They scavenge for food, helping them grow and prepare for the next phase of their life cycle.

Pupal Stage

As spider beetles reach the end of their larval stage, they form a cocoon and enter the pupal stage. Inside the cocoon, the larvae undergo a complete metamorphosis, transforming into adult spider beetles.

Adult Stage

Once the metamorphosis is complete, the adults emerge from their cocoons. Adult spider beetles are generally small, ranging between 2 to 5 millimeters long, and can be dark brown or light brown in color. They have long legs, which gives them a superficial resemblance to spiders.

In the adult stage, spider beetles continue to scavenge for food and mate. After mating, the females lay eggs, and the cycle begins again.

Optimum Conditions for Growth

To ensure successful development from egg to adult, spider beetles require specific conditions. This can include factors such as:

  • Humidity: High levels of humidity are crucial for the hatching of spider beetle eggs.
  • Temperature: A moderate temperature range is essential for the beetles’ growth and reproduction.
  • Food sources: As scavengers, spider beetles need access to materials like dried plants, grains, and other organic debris.

By providing the proper environment, you can help support the healthy growth of spider beetle populations.

Spider Beetle Diet

Spider beetles have a diverse diet that varies depending on the species and their environment. They can be found in a variety of locations such as households, warehouses, and other areas where food is stored.

Their primary food sources include:

  • Stored foods: Spider beetles are known to be pests that infest stored food products. They have a preference for grain-based items, but they can also consume other types of food.
  • Seeds: These beetles enjoy consuming different types of seeds, which are abundant in various food storage environments.
  • Dried fruits: Dried fruits like raisins and dates are also part of a spider beetle’s diet.

Other food sources they might consume are:

  • Grains: Bowls of rice, flour, and other grains are attractive to spider beetles. They can infest these items and make them unfit for human consumption.
  • Dead insects: Some species of spider beetles feed on dead insects, making them a form of natural pest control.
  • Spices: They are also known to infest spices, affecting their flavor and quality.

As scavengers, they can consume a variety of animal by-products:

  • Wool and feathers: Spider beetles sometimes eat wool and feathers, which can be found in clothing and bedding materials.
  • Animal remains: In some cases, spider beetles can feed on animal remains like carcasses and bones.

To sum up, spider beetles are adaptable feeders that can consume a wide variety of food items. Their diet is mainly based on stored foods, seeds, and dried fruits; however, they can also eat grains, dead insects, spices, and various animal by-products. It’s important to be aware of their dietary preferences to prevent infestations and protect your stored food supplies.

Spider Beetles as Pests


Spider beetles are common and widespread insects that can infest homes and businesses as stored product pests. They are most frequently found in pantries, storage areas, and warehouses where they feed on a variety of stored food products. Some common examples of products they infest include cereals, grains, dried fruits, and even non-food items like pet feed and stored textiles. As a result, they can be a source of household pests and may even contaminate your stored items.

Damage Caused

When spider beetles infest your stored products, they can cause various types of damage. Their feeding habits may lead to:

  • Contamination: When these pests infest food items, they can leave behind feces and body parts, contaminating the product and making it unfit for consumption.
  • Piercing: Spider beetles, like the biscuit beetle, may create tiny holes in packaging materials as they chew through to reach their preferred food source.
  • Food spoilage: As they feed on your stored items, they may facilitate the growth of mold and other pathogens that can lead to spoilage.

Conducive Conditions for Infestation

Understanding the factors that contribute to spider beetle infestations can help you better manage these pests in your home or business. Some conditions that determine the likelihood of infestations are:

  • Temperature: Spider beetles thrive in temperatures between 65°F to 80°F (18°C to 27°C) and prefer dark areas with moderate to high humidity levels.
  • Food sources: Abundant food sources like stored grains and dried fruits can attract spider beetles to your home or storage facility.

In summary, be cautious of spider beetles as pests due to their infestation habits, the damage they can cause to stored products, and the conditions that favor their presence. Addressing these factors through proper storage techniques and pest management can help keep these insects at bay and protect your stored items.

Handling Spider Beetle Infestations

To control a spider beetle infestation, start by thoroughly cleaning the infested area. Remove any clutter and wipe down surfaces to eliminate potential food sources and hiding spots for these pests. Vacuum all corners, cracks, and crevices as this will help to remove eggs, larvae, and adult beetles from the environment.

  • Control: Implement preventative measures such as properly sealing and storing food items, disposing of trash regularly, and maintaining a clean and clutter-free living space.
  • Cleaning: Regularly clean areas where you have found spider beetles, paying particular attention to floors, shelves, and corners.
  • Vacuum: Use a vacuum cleaner with a strong suction to remove spider beetles from carpets, furniture, and other surfaces where they may be hiding.
  • Airtight containers: Store your dry goods, such as grains, cereals, and pet food, in airtight containers to prevent spider beetle infestations.

In addition to these steps, consider using natural methods to combat spider beetles. Introduce beneficial insects such as predatory mites or rove beetles in your garden to help keep spider beetle populations under control.

Here are the pros and cons of using natural control methods:

Pros Cons
Environmentally friendly May take longer to see results
Non-toxic to humans and pets Requires careful monitoring
Targets only specific pest populations Effectiveness can vary depending on factors

Remember, maintaining a clean and well-organized living space is key in preventing spider beetle infestations. By following these tips and staying vigilant, you can effectively manage and control spider beetle populations in your home.

Biological Classification

Spider beetles belong to the Animalia kingdom, as they are multicellular organisms that consume other organisms for sustenance. Like other insects, they are part of the Arthropoda phylum, which consists of invertebrates with exoskeletons, segmented bodies, and jointed appendages.

In particular, spider beetles are under the Insecta class, characterized by having three body segments, a pair of antennae, and three pairs of legs. Spider beetles earned their name because of their superficial resemblance to spiders, with long legs and oval or cylindrical bodies.

Here is a brief comparison of the three main taxonomic groups:

Taxonomic Group Characteristics Examples
Animalia Multicellular, heterotrophic organisms Mammals, Birds
Arthropoda Invertebrates, exoskeletons, segmented bodies Insects, Spiders
Insecta Three body segments, antennae, three pairs of legs Beetles, Flies

To recap, spider beetles are part of the Animalia kingdom, Arthropoda phylum, and Insecta class. This gives them features such as being multicellular, having exoskeletons, and sporting segmented bodies. Thus, they exhibit the long legs and distinct body shape reminiscent of spiders while actually being classified as beetles.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Spider Beetles


Apartment Bug – Manhattan NYC
April 12, 2010
Hi Thanks for your help! I live in a newly renovated apartment in Manhattan, New York and keep coming across these bugs. (image attached). I am concerned that they might be ticks or bed bugs? I usually find them crawling the walls, but found a bunch in a light fixture. Any help identifying them or any risk they may pose? Thanks so much!
Bob from NYC
West Harlem, New York, NY

Spider Beetles

Hi Bob,
You have a sizable infestation of Spider Beetles, Gibbium aequinoctiale.  You should check your stored foods as they often infest items in the pantry.

Letter 2 – Spider Beetles


bug found in bed!!! not a bedbug but still wtf!!
Location: in the basement of a house in Denver, Co.
October 28, 2010 6:48 pm
hey guys,
i found these two in my sheets one morning. they freaked me out at first but after looking through the archives on your site, im confident they’re not bedbugs. they’re reddish brown, have six legs spanning only 5mm, and have a glossy round abdomen thats only 2mm wide. they look like miniature weevils to me. sorry about the weak picture but the macro setting on my cell phone sucks. what do you think?
Signature: Michael

Spider Beetles

Hi Michael,
These are Spider Beetles in the genus
Mezium which you can verify on BugGuide.  According to BugGuide, the habitat includes:  “mammal/bird/bee nests, dry carrion, tree holes; several species occur in homes, granaries, mills, warehouses” and it seems that beds can be added to that list since your letter is not the first report we have gotten of Spider Beetles found between the sheets.  Perhaps you should stop eating crackers in bed since Spider Beetles are most commonly associated with infestations in the kitchen.

Letter 3 – Spider Beetle, not Bed Bug


help identifying a bug
Location: New York City
November 27, 2010 9:33 pm
Can you tell me what type of bug this is – see 2 attached photos.
I was told it was a carpenter beetle but it does not seem to match the photos online. I am concerned it might be a bed bug.
I apprecaite any help you can offer.
Signature: ds

Spider Beetle

Dear ds,
It is our casual observation that in recent years, Bed Bug Paranoia has reached epidemic proportions and it affects far more people than actual Bed Bug infestations affect.  Every imaginable household intruder or household visitor becomes suspect as Bed Bug infestation coverage saturates the media.  We in no means intend to disparage the media for attempting to make the public aware of a possible health crisis, but the fallout to the information has the public flocking to extermination services in situations that would be better remedied with a thorough cleaning of the kitchen cupboards.  Your creatures are NOT Bed Bugs.  They are relatively harmless Smooth Spider Beetles,
Gibbium aequinoctiale, which according to BugGuide, is found “Mainly in houses, flour mills, occasionally in warehouses, hospitals, and stores”.  BugGuide also indicates:  “This species is a scavenger, feeding on a wide variety of dead plant and animal materials.  It has become a pest by feeding on dry stored products.”   We would recommend that you search for the source of the infestation, including possibly stored flour products that have been on your kitchen shelf for more than a year, that jumbo size of pet food that saved you $2 but takes Fido a year to consume, or even the cookie crumbs that have fallen between the couch cushions.  Standard extermination services often do nothing to eliminate pantry pests like Spider Beetles because the actual food is not sprayed with the insecticide.

Letter 4 – Spider Beetles


What is this little bug? (please help)
Bugman please help!
I live in Philadelphia and I keep finding these bugs in my apartment. I thought they were biting me but I am not sure. I have never seen anything like these things before in my life. Enclosed are two photographs of these bugs. I found them near my bed, which makes me terrified to sleep in it. They are round and shiny like tiny beads and are amber-reddish in color. They have those little legs and they are almost always dead when I find them. Also, when they are held up to the light they are translucent.
Scared in PA!

Dear S.A.,
Fear not. These are Mezium Spider Beetles, grain infesting Pantry Beetles. They will infest your stored food, but will not bite you.

Expert Update: (05/22/2008) spider beetle errors
Dear Bugman,
I believe I had written earlier when looking at many of the spider beetle pictures. Almost all of the shiny brown, globular body, images are of Gibbium aequinoctiale and not Mezium species. There is a combined 2 image photo (finger and beetle & 2 beetles) of Mezium : the answer was posted by Eric Eaton, I believe. Gibbium species do not have a velvety covering on the thorax, Mezium species do. You should correct your website postings so people will have a better idea of what they have been finding. Best regards,
Louis N. Sorkin, B.C.E.
Entomology Section
Division of Invertebrate Zoology
American Museum of Natural History
New York

Dear Lou,
Thanks so much for resending this vital correction to our website. We really appreciate your expertise on this. We sincerely hope that addressing you with such familiarity doesn’t detract from your professional status.

Letter 5 – Spider Beetles


bug info
We are having this bug on our carpet for a while. Apparently it’s harmless, but since I have a 6-month-old baby, I’d like to check what it is. I’ve looked at several bug pictures, but could not find it. We also find them sometimes on our bathtub. We live in Boston, MA. It is the size of a small ant, very small. To kill it, I crush it and it sounds like killing a pregnant dog’s flea, it cracks. I’ve put a couple in a completely closed jar a few days ago, and they are still alive. I’m sending some pictures I took. I’d appreciate any kind of information you could provide me.
Thanks a lot
Melina Suarez

Dear Melina
We were not sure exactly what species of beetle you had, though we suspected some type of Pantry Beetle. We contacted a true beetle expert, Eric Eaton who gave us the following reply:
“Some pretty clear images of pretty tiny beetles! They are spider beetles, Mezium americanum. It is a stored product pest, so best to inspect the pantry to find the source of the infestation. This should also include examination of pet food, taxidermy mounts, insect collections, the spice rack….Aside from adding some inadvertent protein to one’s diet, though, they are of no real consequence even if you don’t ever find them. Aside, we’d love to have these images submitted to Bugguide.net. Not even sure this family is represented yet.
Ed. Note: We put Eric in contact with Melina and hopefully she will give permission to post the images on Bugguide.net.


  • 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.

7 thoughts on “Spider Beetle Life Cycle: A Closer Look at These Intriguing Insects”

  1. It’s been my understanding that spider beetles eat feathers. Do you have a down comforter? That’s my theory on why they turn up in people’s beds. I have pigeons living outside my window which I’m sure is the source of my SB problem in my bedroom as it gets hot and I have to leave the window open sometimes. I believe a few must have gotten into the bedroom and started breeding- sure enough I began finding several in my bed and put two and two together.

  2. I suspected dust mites.I called an extermi nator and he sprayed for dust mites without confirming it. I have been using allergy wash for dust mites only to still feel pinches in my clothes. I had the carpet and furniture steam cleaned. I still had a problem. My apartment complex extermi nator came three times and was not c onvinced it was dust mites but something was going on. He put traps in the living room and bedroom. He caught what he says is a spider beetle. He is coming to treat for this Wednesday. However, I washed my clothes in regular detergent and still get pinches from my clothing. I told maintenance that I think I have bed bugs because something that pinches still lives in my carpet and at night in my sheets. I do have some bite or allergy marks on my chest and have been to 3 doctors. I am awaiting an allergy test. I read that spider beetles do not bite. I got a bite on my upper foot that went right into my vein and left a black and blue mark. I can feel them pinching me and biting. Maintenance does not think it is bed bugs although we had an infestation problem in other apartments. I had my carpet and furniture steam cleaned but still have a problem when I frequent certain places where I sit on a wooden chair. Something comes on my shoes and up my legs. I have been washing my bedding and clothes putting them in trash bags and when washed and dried I put them in clean trash bags. I can’t sleep and have no apetite. I lost 18 pounds within this 7 week problem. I am told to still isolate my laundry until I can talk to the extermimator Wednesday. I know that spider beetles and bed bug symptoms are closely related. But I still believe I have bed bugs. I vacuum every day, have seen no bugs but have found what look like beetles . It has cost me a lot so far and I am so anxious to find the source of the problem.

  3. Spider beetles do bite !!! How did I know that I ‘Ll tell you my story , one day wile slipping I felt a stinging bite it was so painfull I smash my hand against my right arm and run to the bathroom so the bug has no chance to escape , and then came the surprise it wasn’t a bed bug it was a spider beetles !!!! I have seen them around several times in my previous apartment mainly in the bathroom I was thinking they are harmless and never had any problem until now , I’m really scared now I bought a net with tiny holes to close the vent and other opening in the bathroom .

  4. One time I found one of these crawling on my laptop, clearly alive. Slow moving, but moving nonetheless.

    I started poking at it and then it ‘died’ or at least immediately started playing dead. Make sure you kill them good cause I think this is a defense mechanism or something.

    I pretty much just poked it with my pencil to try safely transferring it. Looked like it was trying to crawl onto it, but then it just fell over and wrapped its legs up.

    Once again, if you’re killing them, make sure they’re dead.

  5. Been in this home for 20+ years and never saw one until we decided to move. Took out the King bed, vacuumed the carpet, and now have seen 4 or 5 in just two days. One was on me this morning while I was in bed. (We put a different bed in its place.) So I am searching for answers. One, above, comments about an open window. There is one right over the bed we keep open at night. idk. This is strange. No food in bedroom. Just bedroom furniture. Granted, not moved in a LONG TIME. Weird. Creepy things look like they are full of blood.


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