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.
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?
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.
Treatment for Bites
Immediate action in case of a black widow bite involves:
- Washing the bite area with soap and water
- Applying a cold compress to reduce pain and swelling
- 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
14 Comments. Leave new
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
The same thought did cross our mind.
Just as clarification, the picture is of the Redback spider, a black widow endemic to Australia (Latrodectus hasselti).
Thanks for the correction
Nice picture. Nice spider-looking, that is, but not if you touch.
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.
Luckily Black Widows are not aggressive spiders.
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.
I found one exactly like that in my yard in Michigan. :/ Not to happy to find out it was a black widow.
I just found this exact spider on the back of my house in Charlotte NC. Beautiful!! Gonna leave it alone ……
Just be aware that the venom of a Black Widow bite can pose a danger to young children and the elderly.
Outstanding! In snakes I believe the more. colorful, the more dangerous, If true in some spiders are these very dangerous? Beautiful colors!
Male Black Widow Spiders are not considered dangerous to humans, unlike the bite of a female which can cause severe medical reactions.
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?