Spider Beetle: All You Need to Know – Your Friendly Guide

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.

Footnotes

  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

  5. Source

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 – Why are Spider Beetles in the Toilet???

 

Subject: Click clogged and found bugs
Location: New York City
August 13, 2015 11:28 am
I just moved into a new apartment in Brooklyn, New York – NYC. The apartment was refernished about 2 years ago. When I moved into the aparmtent, the bathroom sink was clogged and asked the superatendent to fix it. When I came home I found these bugs in the toilet. Can you indicate what bugs these are? I believe they have only 6 legs, and look similar to bed bugs or a spider.
Signature: Any way

Spider Beetles
Spider Beetles

Dear Any way,
We are a bit confused about the connection between the clogged drain and your discovery in the toilet because we can’t imagine the superintendent leaving them there if they were removed from the drain.  Do you suspect that in unclogging the drain, the water came up in the toilet and that these insects were the cause of the clog?  While the circumstances are quite confusing, we can tell you that the insects you found in the toilet are Spider Beetles in the Subfamily Ptininae, and that they infest stored foods and will eat a wide variety of organic substances in the home.  According to BugGuide:  “several species occur in homes, granaries, mills, warehouses.”

Spider Beetles
Spider Beetles

Letter 2 – Spider Beetles and Larva

 

Please identify these bugs!
Hello Again,
I am very anxious to ask you what are the bugs that I’ve attached. For me, but I am almost too upset to go into the full story of how and how many of these bugs I’ve found in my NYC apartment. I fear that they may be bad for my health. Can you please help me identify, or tell me what they are not. No one’s been able to help me.
Sincerely,
Russell Cowans

Hi Russell,
You have Spider Beetles, Mezium species. According to the Audubon Guide: “These minute, pear-shaped beetles superficially resemble spiders because of their long, thin legs and long threadlike antennae. Most are brownish and less than 1/4 inch long. … Both adults and their C-shaped larvae are scavengers, feeding on dried organic matter, including wook, museum specimens, desiccated animals,l dung, plants, stored seeds, and dried fruits. … Continuous generations as long as food remains available.” So, you had better find the food source. They will not harm you except for your sanity. Good luck.

Hello, It was sure good to hear back from you. I have one question though; do you really think the larvae in the picture is that of the beatle. Dare I say it; after moving into my brothers room, a room which was not clean out for some time-in the bottom corners of a very warm closet, in a dust collection I found scores of shed skin and living larvae. I would come to find this scene in various spots of my house. One area turned up the larvae always in a much smaller state-the bathroom, in particular; by the cat litter. I decided to examine the cat food box (newly bought from the local store) remembering what I read about meal worms etc. I turned over an entire box into my bath tub so that the white background would allow for easy detection of critters, I wasn’t completely surprised to see that out (along with the food) came baby larvae, fast movers, but poor on slick surfaces like a tub. Also, this would be the first time I came across black beatle like bugs. I wondered was the larvae that of the beatles and began wondering if they were spread by my cat! Online, the closet pictures to the black beatles I found and their larvae was a name of Tenebrio beatle and grain beatles? I wondered if I was dealing with two different bugs because, the red little guys I found long after the larvae. Around the time I found the attached picture, this is taken beneath my window sill, the red dots are too small for me to discern any recognizable features, only that I never found them moving always dead or still and they’ve shown up twice. I don’t know what they are/were. Funny, I moved into the living room onto a beach chair to get some sanity, I’m pretty sure they’re back by now.
Russell C

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,
Lou
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 3 – Spider Beetles

 

Small Dark Red Tick-like Bug
Location: Chicago, IL, USA
May 4, 2011 9:28 am
I’ve found 3 of these bugs in my house within the last month (2 in a bathtub and 1 in a closet), but never before. Maybe it’s the warm weather? I thought they were ticks, I have two cats, but their extremely brittle/fragile. I killed the only live one I’ve found by accident when trying to trap it. They have a bulbous body that’s dark red, so I thought it would store blood, but it’s hollow and I can see through it. Thanks for your help and time!
Signature: TC

Spider Beetles

Dear TC,
You have Spider Beetles, a common pest of stored foods.  Check the pantry for the source of the infestation.

Letter 4 – Spider Beetles and Dermestid Larva

 

Please identify these bugs!
Hello Again,
I am very anxious to ask you what are the bugs that I’ve attached. For me, but I am almost too upset to go into the full story of how and how many of these bugs I’ve found in my NYC apartment. I fear that they may be bad for my health. Can you please help me identify, or tell me what they are not. No one’s been able to help me.
Sincerely,
Russell Cowans

Hi Russell,
You have Spider Beetles, Mezium species. According to the Audubon Guide: “These minute, pear-shaped beetles superficially resemble spiders because of their long, thin legs and long threadlike antennae. Most are brownish and less than 1/4 inch long. … Both adults and their C-shaped larvae are scavengers, feeding on dried organic matter, including wook, museum specimens, desiccated animals,l dung, plants, stored seeds, and dried fruits. … Continuous generations as long as food remains available.” So, you had better find the food source. They will not harm you except for your sanity. The larva is a Dermestid, possibly a Carpet Beetle. Good luck.

Letter 5 – Whitemarked Spider Beetles

 

Subject: white spotted spider beetle
Location: Nova Scotia
November 26, 2012 12:29 pm
I do not see this bug species on your site. I have a problem with it. It recently appeared from a void in the BR, under the vanity. Quickly becoming a pest I have to deal with. Crawling bugs are controlable but flying is a problem. Has been identified; sharing photos; hope they come thru. I have seen egg, partially developed, crawling and flying. Is not in my kitchen or food. Does not bite, but the flying ones burn like a no-see-um if they light on me. I do not know how it got here, must have come on store products. Could almost miss the flyers for fruit flies. How prevalent are they in Canada?
Signature: Bugged

Whitemarked Spider Beetles

Dear Bugged,
Since we did not know this species, we looked it up on BugGuide and believe you are speaking of the Whitemarked Spider Beetle,
Ptinus fur.  BugGuide indicates it was:  “introduced to NA before 1870.”  BugGuide reports sightings in Ontario and the United States across the border.  Thank you for adding to our archive of Household Pests.

Whitemarked Spider Beetles

Is that really a photo of the egg?

Whitemarked Spider Beetle Egg, we suppose.

These photos surprised me when I enlarged them as it looks like a spec on the sticky paper of the monitor box I photographed. It is certainly some stage of development. I thought it had started to change color on one end?  Have not seen any nests or fuzzy pupae they describe in some writing and the “fur” is not evident without magnification, they are very small to start.  Am certain these are the developing ones.  In the further monitoring I checked yesterday there is a fully developed winged one, looks much like a common small housefly, plus there is the first I have seen that shows the spotted body really well (female?).  I will try and get a decent photo of that box.  I got the ID through Orkin pest control who contacted their lead entomologist at their Quality Control.
“It is white marked spider beetle. There are differences between females and males looks. The white patch may not always be the same.”
The worst of this specific one for control is that it flies.  I am not sure how it arrived, but I did buy a new sisal cat scratch post from a pet store in Oct.. and it sat on the floor on the opposite side of the bathroom wall, BR being where they emerged.  I have no carpets.  They are not in the kitchen, BdR or living room except a rare crawling one killed early on.  But they have moved into the basement and I see very few in the BR now.
I was surprised to find that of the ones caught on paper first (in the pictures I sent) and placed in a ziplock bag, some still had faint life a week later.  They are extremely hardy.
Carol

Update from Carol January 3, 3013
Hi Daniel:  Sorry to be so long getting this done.  In 1271 note there is an egg in the 4 o’clock position.  It is quite round and black when the picture is enlarged and in Picasa3 which I use I tried to correct the blur and it just went quite black so I left it untouched.  Enlargement is not as clear as it should be but it is the camera.
Would like to say these beetles seem to go on to become some version of a small fly from what I can tell.  There is no evidence they came on the cat post I mentioned.  I believe myself they either came on clothes from the line stored under the cabinet or under the siding and followed the double beam across the house.  I did see ants going there during our very hot dry August and got them but this could be from the same area.  No other explanation comes to mind.
I have had pest control once a few weeks ago.  They are gone now from upstairs, but not gone entirely from the basement and PC will come again to redo.  I am hopefully optimistic they will be eradicated but it is a real problem as they are so minute and even microscopic as some of this I could not see until photographed… more that I ever wanted to know about them!
regards,
Carol
http://home.cc.umanitoba.ca/~fieldspg/fields/beetles.pdf
Beetles Identification Guide
Ptinus fur (Linnaeus)
whitemarked spider beetle
ptine bigarré
Diagnosis: The species is distinguished from the other Ptinus included here in
having 2 tufts of setae on the pronotal disc, with the surface between the tufts
dull, punctured, and granulated.
Sexual dimorphism: Males (Fig. 224) have the elytra subparallel-sided, the eyes
larger and more convex, the antennae longer (10th segment about five times as
long as wide), the tufts of setae on the pronotal disc less defined, and the
metasternum longer and convex. Females (Fig. 225) have the elytra subobovate,
the eyes smaller and less convex, the antennae shorter (10th segment about
twice as long as wide), the tufts of setae on the pronotal disc more defined, and
the metasternum shorter and flat.
Distribution: Reported from Europe, North Africa, Asia, New Zealand, and
North America, where it was introduced before 1870. In Canada the species has
been collected in all provinces.
Economic importance: In Canada, this species is found mainly in warehouses
and dwellings, less frequently in museums, granaries, and grain elevators. It is
one of the most commonly reported ptinids in British Columbia.
Ptinus ocellus Brown (synonym: P. tectus auct.)
Australian spider beetle
ptine ocellé
161
Fig. 224 Ptinus fur (Linnaeus); male. Scale = 0.5 mm.
162
Fig. 225 Ptinus fur (Linnaeus); female. Scale = 0.5 mm.

 

Authors

    by
  • 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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