How Big Can Black Widow Spiders Get? Uncovering the Surprising Truth

Black widow spiders are known for their potentially dangerous bite and unique appearance.

These fascinating creatures can vary in size, with the females generally being larger than the males.

Female black widows can reach about 3/8 inches (8-10 mm) in size, excluding their legs, while males tend to be smaller at about 1/8 inches (3-4 mm).

These spiders come in different species, with one example being the Northern Black Widow Spider (Latrodectus variolus), found in the eastern US and parts of Canada.

Immature, female Northern Black Widow

Their size difference becomes more apparent when including their legs, as females can measure up to 1½ inches.

On the other hand, male spiders are characterized by a much thinner body frame, approximately 1/4 inch excluding legs.

The Basics of Black Widow Spiders

Species of Black Widow Spiders

There are several species of black widow spiders, belonging to the genus Latrodectus.

  • Latrodectus mactans: Southern black widow, found in North America
  • Latrodectus hesperus: Western black widow, found in western North America
  • Latrodectus variolus: Northern black widow, found in eastern North America
  • Other species can be found in South Africa and other parts of the world.

Physical Characteristics

Black widow spiders are known for their distinctive appearance. Some common characteristics include:

  • Female black widows are usually larger, with a body length of 8 to 13 millimeters and 25 to 35 millimeters when their legs are extended 1. Males are smaller and do not have the same markings.
  • A glossy, black body with a red marking on the abdomen.
  • The famous hourglass-shaped red marking on the underside of the female’s abdomen, which differs between species 2.

Habitat and Distribution

Black widow spiders can be found in various habitats, such as:

  • Woodpiles
  • Undisturbed areas
  • Basements
  • Garages

They are known to inhabit every US state except Maine and can also be found in Canada, Mexico, and South Africa 3.

Here’s a comparison of the common black widow species:

Species Distribution Hourglass Marking
Latrodectus mactans Southern North America Complete hourglass
Latrodectus hesperus Western North America Connected triangles
Latrodectus variolus Eastern North America Separate triangles

How Big Can Black Widow Spiders Get
Immature Western Black Widow

How Big Can Black Widow Spiders Get?

Female Black Widow Size

  • Size: Female black widows are larger than males, with a body length of 3/8″ (8-10 mm) 1.
  • Identification: They have a shiny black body and a red hourglass-shaped marking on the abdomen 2.

Male Black Widow Size

  • Size: Male black widows are smaller, measuring only 1/8″ (3-4 mm) in body length 3.
  • Identification: Males have an elongated abdomen with white and red markings on the sides 4.

Comparison Table: Female vs. Male Black Widow

Features Female Black Widow Male Black Widow
Size 3/8″ (8-10 mm) 1/8″ (3-4 mm)
Markings Red hourglass on abdomen White and red markings on sides

Venom and Bites

Effects of the Venom

The black widow spider’s venom affects the nervous system, causing symptoms such as:

  • Muscle aches
  • Nausea
  • Paralysis (in severe cases)

A black widow bite can lead to an increase in blood pressure, heart rate, and breathing difficulties. The venom consists of a neurotoxic protein known as alpha-latrotoxin.

Venom Production and Potency

Black widow spiders have potent venom, which is:

  • 15 times more toxic than rattlesnake venom
  • Injected in small amounts during a bite

Comparatively, here’s how the venom potency stacks up:

Spider Type Venom Potency
Black Widow Spider 15x (Rattlesnake venom)
Rattlesnake 1x

They produce the venom in their abdomen.

Immature Northern Black Widow

Treatment for Bites

Immediate action in case of a black widow bite involves:

  1. Washing the bite area with soap and water
  2. Applying a cold compress to reduce pain and swelling
  3. Calling a poison control center or seeking medical attention

A physician may administer antivenom in severe cases. According to National Geographic, antivenom has drastically reduced the number of severe incidents related to black widow bites.

Pros of Antivenom:

  • Counteracts the venom’s effects
  • Reduces pain and risks of complications

Cons of Antivenom:

  • Possible allergic reactions to the medication

Conclusion

Black widow spiders, renowned for their venomous bite and unique appearance, exhibit significant differences between males and females in size, markings, and behavior.

With various species spread across North America, they’ve adapted to diverse habitats and have a specialized diet and hunting technique.

While their venom poses a threat to humans, understanding their habits, and habitats, and taking preventive measures can mitigate risks.

Recognizing their relatives and look-alikes further enriches our knowledge of these intriguing arachnids.

Footnotes

  1. Penn State Extension 2
  2. Missouri Department of Conservation 2
  3. Texas A&M University 2
  4. Black Widow | Department of Entomology | Washington State University

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 – Widow with Hearts!!!!! Southern Belle

beautiful tennessee spider
Hello,
This is actually a re-posting* so I can provide more information in hopes that you’ll be able to identify this beauty. Picture was taken June 11, 2005, in Crossville, TN (Cumberland Plateau area) in a wooded area. The spider’s body is very shiny black, hairless and a little smaller than dime.

I’ve looked everywhere on the web and can’t seem to find it. The Australian Red-back comes close, but what would that be doing in Tennessee?? Hopefully, you can solve this mystery.
Thanks,
Melinda Z

*I showed the picture at a friendly gathering last night and in the heat of the moment, my friend sent you the picture without much info. We all really want to know what kind of spider this is!

Hi Melinda,
Over the years we have gotten letter describing a spider that looked like a Black Widow but with hearts on its back. Yours is the first photo we have received substantiating this. Of course, it does look exactly like a Black Widow, but we could find no information on the Heart shaped markings.

So, when in doubt, we wrote to Eric Eaton. Here is his response: “This is indeed a black widow, the Southern Black Widow, Latrodectus mactans. Many females have red markings on the top of the abdomen like this. The hourglass mark is on the UNDERSIDE, so apparently the folks who say there is no hourglass hadn’t looked at the belly of the beast:-)

Additionally, Northern Black Widows, L. variolus, have a broken hourglass on the belly, and often red stripes and spots on the back. They are generally smaller than other widow species. Lastly, widows begin as WHITE spiderlings with various darker markings.

As they age they darken, but may retain several red markings. Older individuals may have few if any markings other than the hourglass. Female widows may easily live two or more years in the wild. Hope this clarifies. Eric”

Thanks for the quick response. It’s a black widow after all: southern bell!!

Letter 2 – Redback Spider from Australia

black and red spider
Location: North East USA
October 25, 2010 8:18 pm
Dear Bugman, I beg of your help. I am finding these red and black spiders (i believe) in the house. I live in CT. These bugs are so tiny maybe the size of a grain of rice.

The first thing you notice is a little glossy redish black ball. I only find them on the rugs, havent seen them elsewhere. I have two new babies and I am soooooo scared. I dont have a camera to take a picture but I pray you can still help us.
I provided a picture of the closet spider i can find, this resembles the body structure but not the color or size.
Signature: BR

Redback Spider

Dear BR,
You do have some cause for concern if your creatures are the same as the one in the photo, though we have our doubts since you did not provide your own photograph.  This is an immature Black Widow. 

Black Widows are one of only a few North American spiders with a dangerously venomous bite, and young children would be more severely affected by a bite than a healthy adult would.  Again, we really doubt that the creatures you have found are Black Widows.

Ed. Note: It has been brought to our attention in a comment that the spider in the photo is most probably not a North American species, but a mature Redback Spider from Australia, which is why the location in which a creature is encountered is often critical information for proper identification.

i cannot thank you enough for you quick response, I dont believe they are either. The structure is similar but they carry a little ball like on them it allmost looks like a bead, if i look at it very close its a maroonish dark red color.

We have recently discovered we have carpet beetles and i dont know if this may be related, again we find these spiders on the rug and between the rug and wall. any other advice would kindly be appreciated i will try to get a picture to you as soon as i can, you are all wonderful people for doing this for others. thank you again

Letter 3 – Red and Black Mystery Spider: Identified as Male Black Widow

Amazing Mystery Spider and other Arachnids
Hello to a marvelous site, Let me state right up front that I find your site to be interesting, informative, entertaining and helpful. I have enjoyed looking at the photos and reading the data that you and others provide.

As a new-comer to digital photography in general (and bug close-ups in particular), your site has been a gold mine for helping me identifing many of the small creatures I have photographed. I looked at every spider photo you have and nowhere have I seen anything that resembles the Mystery spider I found this past spring.

I have googled every variation of “red and black spider, red legged spider, colorful spider, etc.” that I could think of with no success. I am hoping you will be able to help me with this puzzle. I am also including a small variety of other spider pics I have taken. I am not sure which species the jumping spider is but I think the garden spider is some variety of an Argiope, and that the Green one is a Lynx spider, (by the way, the wasp lost, lol).

They are some of my better spider captures and I thought you might find them acceptable or useful for posting. This is the third time I have attempted to get a response from your site and maybe the third time will be charmed, lol. I realize that you can’t answer all the submittions you receive but I am counting on perserverance to accomplish my identity search for this very unusually shaped and colored spider.

BTW – I am in the northeast corner of Texas and the leg span of the red and black spider was several inches across as can be seen in the image where it is on a cone flower. This is the first and only time I have ever seen this type of spider.
Lee R.

Hi Lee,
Wow, what an awesome looking spider. It is a mystery to us as well. We are going to try some searching in the Lynx Spider Family Oxyopidae, and perhaps some Arachnid expert will know what this is based on our posting. We are sorry we have not responded to your prior letters.

It is nothing personal. It is just impossible to even read all the mail we receive. Eric Eaton provided this assessment: “Gee, the photo doesn’t come across very well on my WebTV, but I think the spider is probably a male of either Nephila clavipes or one of the species in the genus Argiope. Just an educated guess, though.”

Update: (05/07/2007) Mystery spider…
Hi,
Gary here, from the Missouri Ozarks. “Lee” posted a photo on your site dated September of 2006 taken in Northern Texas of a colorful spider that had red and black legs, a black body with red markings on it’s back.

You folks told him you didn’t know what it was. Well, I’ve found a match for it in my wife’s office and according to the University of Kentucky’s Entomology website (“Mystery Bug” section) it is a male black widow. I hope this helps. R/S
Gary Paddock
Shell Knob, Mo.

Letter 4 – Western Black Widow Family Values

A rare treat, Western black widow male, female, and eggs in one photo!
Adult female, eggs and male – Latrodectus hesperus – Male Female El Mirage AZ, Maricopa County, Arizona, USA September 6, 2006 An adult female with egg sacks, and a closeby male.

I could not believe she was staying put, maybe because she was guarding her eggs, she was quite alarmed at me. This is one of 4 adult females in my yard that I have found. Most of the time they run and hide when I approach. This was a treat!
Candy Cox

Hi Candy,
Thanks for sharing this wonderful domestic moment with our readership, many of whom appreciate family values. We are also thrilled to find there are others out there without widow phobia.

Letter 5 – Western Widow

Black Widow?
Hello!
Just wondering if you could confirm for me if this spider is in fact a black widow? It was found in Victoria BC, under a rock. As you can tell from the second photo, it was found with a messy web made of a really strong web material. It didn’t have an hourglass on the abdomen, and only had one orange mark, not two as the northern black widow is reported to have.

Hi Vanessa and Colin,
There is often a degree of individual variation when it comes to coloration and markings. This is a Widow, and Eric Eaton informs us it is a Western Widow. Thanks for sending in such marvelous photos.

Letter 6 – Widow’s Mate: Male Spider

Juvenile Western Black Widow?
From the information I was able to find on the web, it looks like I may have found a Western Black Widow (juvenile) is it possible to make that determination from the attached photos? Hope they are clear enough.
Scot

Hi Scot,
This is a male Western Black Widow. The photos are wonderful.

Authors

  • Daniel Marlos

    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.

14 thoughts on “How Big Can Black Widow Spiders Get? Uncovering the Surprising Truth”

  1. My guess would be that BR is finding spider beetles, a completely harmless and fairly common household creature. They closely resemble the description she gives, having glossy, reddish, ball-like bodies. And even though they are in fact tiny beetles, they do of course resemble spiders, hence the common name.

    Susan J. Hewitt

    Reply
  2. We recently found one of these on our tent while camping in Arkansas. We were hoping it was an impersonator, but thanks to this post we now know it was in fact a black widow (eeks!!). We only saw the three hearts on the back and definitely didn’t play with it to see the hourglass on the underside.

    Reply
  3. I recently found one in Clarksville, TN. I have a pic. I knew it was a black widow, but didn’t see the hearts until after its demise. I hate spiders, but it IS pretty cool to see. Holler at me if you’d like the pic sent to you.

    Reply
  4. I just found this exact spider on the back of my house in Charlotte NC. Beautiful!! Gonna leave it alone ……

    Reply
  5. Outstanding! In snakes I believe the more. colorful, the more dangerous, If true in some spiders are these very dangerous? Beautiful colors!

    Reply
    • Male Black Widow Spiders are not considered dangerous to humans, unlike the bite of a female which can cause severe medical reactions.

      Reply
  6. Yikes, I was just unrolling my halloween flag in the garage and this spider with the hearts on the back was in it! I took a picture. She had 3 red hearts on her back. I tried to flip her over with a leaf to see if there was an hourglass on her belly. Apparently I flipped her too hard because I never saw her again. How can you destroy a spider egg sac or whatever they are called?

    Reply

Leave a Comment