No Tears for the Southern Black Widow
Latrodectus mactans, more commonly known as the southern black widow, is the most common species in the black widow family. While it can be found throughout North America, they are found most often in the southern United States. Within this wide range, L. mactans enjoys a variety of habitats. They prefer areas that are close to the ground, dark, and sheltered; in the wild this may mean dense brush or under logs, while in inhabited areas they may be found in basements, log piles, or under trash lids.
In addition to being the most common black widow, L. mactans is also the largest member of the family Theridiidae. The females are larger than the males, averaging at about 8-10 mm (0.31- 0.39 in) in length and weighing about 1 g (0.04 oz); however the male's legs are generally longer than the females. Both males and females are black, with small thoraxes and extremely large, round abdomens. The female can be distinguished by the iconic red hour-glass shape on the underside of her abdomen, while the male has 4 pairs of red and white stripes on each side of his abdomen.
The southern black widow is mainly solitary, spending most of its time in or near its web. Only the females live long enough to build a web for catching prey, and are the sole source of black widow bites. While bites do require medical attention, no human fatalities have been reported since 1983.
During the day, females hang in the center of the web to expose the bright red warning on their abdomen; when startled they drop to the ground and play dead. Though the webs they construct are haphazard-- the stereotype of cobwebs-- they are extremely strong and are capable of catching woodlice, millipedes, centipedes, other spiders, and occasionally small mice. Once an animal becomes trapped in L. mactan's web, the spider envenoms its prey and wraps it in a thick cocoon. After the animal dies the spider injects it with digestive enzymes and consumes the resulting fluid. Despite their strong venom, the southern black widow can be victim to several predaotrs; namely wasps, the brown widow spider, praying mantises, and large centipedes.
The southern black widow mates primarily in the spring and summer. Mature males build small webs and deposit semen along the threads. He then coats his mouthpieces-- palps-- with sperm and sets out to find a female mate. To court her, he vibrates the threads of her web until she is receptive. On rare occasions, a displeased female may eat the male. Afterwards, if he survives, the male leaves the females web and dies soon afterwards. From just one encounter, the female can store enough sperm to last her a lifetime of reproductive cycles.
After fertilization, the female builds a small web where she lays her egg sac, which can contain up to 400 eggs. She guards these eggs until they hatch about 20 days later, and immedietly disperse to establish their own territories. Until they become fully mature, at about 90 days old, juveniles have no venom and are extremely vulnerable to predators- including adult black widows. Typically only about 30 individuals from a single clutch survive to adulthood. Once mature, males can live for only one year, while females can live up to three years in the wild.
Conservation status: The IUCN has not evaluated the southern black widow, but due to its large range and population size it is considered stable. It is able to adapt to most habitats, and thus the species' only threat comes from extermination via pest control.
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Photos
Mark Kostich
James L. Castner
Meghan F. Murphy
