Southern Black Widow (Latrodectus mactans)

Did you know there’s a spider called the southern black widow? It’s mostly found in North America. It has family members like the western black widow and northern black widow, and they look a bit alike. Want to discover more about this spider? We have some cool facts for you!

Physical Description and Identification

Adult

• Size: Females are mostly 0.31 – 0.51 inches (0.8 – 1.30 cm) long including their leg span while males measure around 0.12 – 0.23 inches (0.3 – 0.6 cm).

• Color: Sexual dimorphism is prominently visible when it comes to coloration. Full-grown female species have a black body, with an hourglass-shaped red marking on their abdomen’s underside. They may even have a red or orange patch over their spinnerets on the abdominal top. The male spiders are purple or even have the grayish-black color of the juveniles.

• Other Characteristic Features: Both sexes have round legs, while females are characterized by a rounded abdomen.

Photo Credit: Tim Martin

Eggs

Female southern black widows create beige-colored egg sacs sizing 0.39-0.49 inches. The sacs release 200-220 eggs, each having a diameter of around 0.03 inches. The incubation period is generally a month after which the spiderlings emerge.

Spiderlings

All spiderlings have a whitish complexion at first which gradually develops into a black shade with every molt. The distinctive hourglass red spot or other marks usually common in adults are also missing in spiderlings.

The juveniles have a gray or white abdomen with orange and yellow spots and white stripes running across.

The Web

Southern black widows create messy three-dimensional webs in the crevices during the day and hang upside down.

Are Southern Black Widow Spiders Venomous?

Yes, Southern Black Widow Spiders are venomous. They have a strong venom that they use mainly for catching food. The females are considered more venomous than their male counterparts as they have larger and sharper mouthparts that can get right into the human skin. Its venom is called alpha-latrotoxin, which causes several neuromotor problems. 

Can Southern Black Widow Spiders Bite?

Yes, Southern Black Widow Spiders can bite. They’re usually not aggressive, but if they feel threatened, they might bite, and it can be painful. Though over two hundred bites have been annually recorded, there have been no instances of death in a healthy adult.

Ecological Importance and Behavior of Southern Black Widow

Southern Black Widows are vital for controlling pest populations, preying on insects such as woodlice, as well as larger prey like mice, millipedes, and centipedes. They play a critical role in their habitats, contributing to the balance of the ecosystems they inhabit.

Natural Predators: Natural predators include blue mud daubers, spider wasps, centipedes, and other spiders like the brown widow. These predators help keep black widow populations in check, ensuring a healthy balance within the ecological community.

Prey-Predator Dynamics: As predators, Southern Black Widows help regulate populations of various arthropods and small vertebrates, forming an essential link in the food web. Conversely, they are preyed upon by specific wasps and centipedes, reflecting the complex interplay of predator and prey within their ecosystem.

Relationship with Humans: While venomous, Southern Black Widows are not typically aggressive toward humans and bite only in self-defense. Their bites can be medically significant, but fatalities are extremely rare. They often dwell in proximity to human habitations, taking residence in undisturbed areas such as rodent burrows, rocks, and woodpiles.

Quick Facts

Did You Know

• Danish zoologist Johan Christian Fabricius described it for the first time in 1775, placing it in the Aranea genus. Later, Charles Athanase Walckenaer placed it in the Latrodectus genus in 1837.

In summary, the Southern Black Widow spider is an important predator with a significant impact on controlling the populations of various invertebrates.