Not long after moving to Riverside from the Midwest, I was messing around in the back corner of the garage, moving old bikes, dusty boxes of holiday ornaments and bags destined for the Assistance League. In the darkness, I spied a shiny black ball, the size of a small marble. It took me a moment to see that it had legs and another to see the red hourglass. Heart pounding, it took me only an instant to realize that I had spotted my first black widow spider.
Everybody knows black widow spiders. They are shiny black spiders with bright red abdominal spots, with the spots most frequently arranged in an hourglass pattern. Everybody knows they are poisonous and dangerous, with a nasty bite. They are not uncommon in California. But that's about all the average Riversider knows. As an average Riversider, I decided to dig a little deeper and learn something of the natural history of these widely feared, but poorly understood, creatures.
First things first. What are we actually talking about? Black widow spiders are members of the "widow spider" genus Latrodectus (the word is a Latin-Greek hybrid meaning "robber-biter"). Latrodectus has about 35 species, including a subgroup known as the true widows. In North America, these include the red widow spider, the invasive brown widow spider and three species of black widow spiders: the northern black widow, the southern black widow and the western black widow.
The western black widow spider, L. hesperus (the "western robber-biter") is common in California's nooks and crannies, just about anywhere it can be undisturbed by light or weather, but with access to its food. Insects ranging from ants to mosquitoes to cockroaches to beetles and beyond make up the black widow's menu. These prey get stuck in the widow's unkempt, but strong and sticky, nets. First, the widow immobilizes the animal by wrapping it in more sticky silk. These small animals aren't going anywhere; ounce for ounce, black widow spider silk is five times as strong as steel. Then the spider bites its dinner item, delivering death by a neurotoxin. It also injects digestive enzymes into the prey's body to liquefy its organs and slurps up the soupy innards. Rarely, they trap and consume small lizards or frogs. Sometimes, not always, the females will consume their pint-sized mates, a likely explanation for the common name, widow.
It turns out that black widow spider bites are not nearly as dangerous as contemporary myth would have it. If you consider their ecology, these inch-long creatures are NOT about to add humans to their diets. Indeed, certain animals actually eat black widows; wasps, birds, shrews, mice and alligator lizards are all black widow predators.
Not all black widows are even capable of biting humans. Only adult females have fangs long enough to pierce human skin. The species is typically shy and smart enough to avoid contact with considerably larger animals. They are only going to bite humans to protect themselves, for example, when they are cornered or flustered. And, of course, females bite to protect their young, incubating in silky, powderpuff-like egg cases. The vast majority of spider species are benign; only a tiny fraction is poisonous. In the case of black widow spiders, the offending neurotoxin is alpha-latrotoxin. Drop for drop, alpha-latrotoxin is 15 times as potent as rattlesnake venom.
But rattlesnake bites are much more dangerous than black widow bites because of the volume delivered by the snake's fangs. Black widows inject only a tiny micro-drop of venom whereas rattlesnakes deliver a relatively high-volume dose. Make no mistake, black widow bites can be quite painful (although the majority are merely annoying). Fatalities, if they occur, are extremely rare. Of over 58,000 recorded black widow spider bites between 1983 and 2009, none resulted in fatalities.
The typical black widow spider bite is similar to a mosquito bite: minor pain and swelling treatable with over-the-counter drugs. The most severe reactions, even if very rare, need more substantial attention. The severe systemic symptoms involve muscle cramps and rigidity, starting near the bite and spreading to the abdomen or back. Pain may be particularly severe in the abdomen. But such bites are exceptional.
It's worth mentioning the western black widow spider's cousin, the brown widow spider Latrodectus geometricus. Originally a pantropical species, the brown widow established a foothold in Southern California around 2000. Its range is expanding and to some extent it appears to be displacing its native cousin. The two species will probably end up coexisting because L. geometricus tends to favor more open environments, such as the undersides of lawn furniture. The brown widow spider is easily distinguished from the black widow. The two species are similarly shaped, but the brown widow is mottled brown and tan with black accents. Its abdomen sports a bright orange hourglass. The brown widow's egg cases are unique in that they have little spikes that make them resemble pollen grains. Bites from brown widow spiders are less noxious than those from black widow spiders. Such bites are typically far less painful. Furthermore, there are no records of fatalities due to a brown widow spider bite.
Among Riverside's various spider species, the shy black widow may be the biggest celebrity. But the mystique of a deadly monster is hardly warranted. Fatalities from black widow bites are vanishingly rare; for comparison, consider that the annual U.S. mortality rate from bee, wasp and hornet stings is 72 per year. Let's just say that black widow spiders turn out to be more interesting and a bit less scary than their reputation warrants.
