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.

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:

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

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 ↩