Black Widow Spider
Latrodectus hesperus

What are black widow spiders?
Black Widow SpiderThe black widow is one of the two dangerous spiders found in the United States. In fact, it is considered the most venomous spider in all of North America. Despite all of this, the mortality rate is actually quite low–less than one percent. So, if you are a healthy person between the ages of 15 and 60, your chances of surviving a black widow bite are very high.

How do I identify one?
The characteristic markings of female black widows (the poisonous ones) are red or yellow hourglass shapes on the abdomens. Their abdomens are jet black, rounded, and globular in shape. Female spiders measure about ½”, and, with their legs spread, 1 ½”. Adult males are half this size, harmless, and have their own unique markings. Besides having longer legs and smaller bodies than the females, the males have yellow and red spots and bands over their back. The immature stages of both sexes also feature their own distinctive markings. When a black widow is newly-hatched, they are white or yellowish white in color and gradually acquire black and varying amounts of red and white with each molt (skin shedding). Young spiders, like the males, are harmless.

What is their life cycle?
Black widow spiders spin webs made of coarse silk. They usually do this in dark places outside near the ground. Occasionally, they are constructed indoors, but usually are spun in trash, rubble piles, and under or around houses and outbuildings. During the course of a summer, 4 to 9 ½” egg sacs are produced. These sacs yield approximately 300 to 400 eggs. However, only 1 in 12 young survive the 2 to 4 week incubation period due to cannibalism.
If the young spiders are able to survive without falling victim to cannibalism, it takes them 2 to 4 months to complete their growth. Females molt 6 to 8 times while males molt 3 to 6 times. All in all, females mature approximately 92 days after egg sac emergence. After maturation, they live approximately 180 days. Males mature 71 days after sac emergence and then have only 30 days of adult life.

Can you tell me a bit about their behavior?
After mating, a female spider will eat the male. The only hope the male has of cheating death is if the female is well-fed (read: ate enough babies). If the male survives another day, he will attempt to mate with another female until his luck runs out and he becomes female food.
Females hang belly upward, rarely leaving the web. Cold weather and drought may drive these spiders into buildings from their outdoor habitat. Female are shy and nocturnal, rarely leaving their hidden webs voluntarily. Typical prey in usually includes cockroaches, beetles, and other insects. So, if you have black widows, you can take comfort in the fact that your insect population is lower than it would be without having black widows.
Outbreaks of black widows occur sporadically. An area may have thousands one year and none the next. In sand dunes areas black widows may be present every year. Seasonal weather and alternating cold and hot temperatures are detrimental to survival.

What if I get bit?
Although the venom of the black widow spider is 15 times as toxic as the prairie rattlesnake, the amount injected during a bite is drastically smaller, thereby making it much less toxic. The mortality for a black widow bite is less than one percent as opposed to the prairie snake’s, which is 15 to 25 percent.
There are several contributing factors that determine the severity of a person’s bite. These include the area of the body bitten, amount of venom injected, depth of the bite, seasonal changes, and temperature. The actual bite feels like nothing more than a pinprick, if it is felt at all. Sometimes, people don’t even know they’ve been bitten.
After a bite, the first symptom may only be a slight local swelling and two faint red spots surrounded by local redness. After one to three hours, intense, agonizing pain begins and may continue for up to 48 hours. Pain usually progresses from the bitten area up or down the arm or leg, finally localizing in the abdomen or back. At this time, the abdominal muscles may become rigid and board-like with severe cramps. Muscles and the soles of feet may become painful and eyelids may become swollen. Other symptoms may include nausea, excessive and profuse perspiration, tremors, labored breathing and speech, and vomiting. The pulse may become feeble and the skin clammy. Unconsciousness and convulsions are possibilities as is the the potential for death if medical attention is not sought immediately. After these symptoms have passed, complications due to infection of the bite-area may occur. In some individuals who do not seek medical attention, symptoms may diminish within several hours or days of agonizing pain. All in all, bites are uncommon and serious injury and death are even less common.
If bitten, try and collect the spider that bit you and remain calm. Get medical attention immediately by contacting your physician, hospital, or Poison Information Center. First aid is of limited help although a mild antiseptic such as iodine or hydrogen peroxide may help to prevent infection.

How do I keep them away?
To prevent black widow spiders from being an unnecessary hazard, remove trash, old boxes, piles of lumber, old rubble piles and other unwanted items from under or around houses and outbuildings. It is not a good idea to walk barefoot or handle firewood and lumber without gloves. To prevent entry into the house, install screens on doors and seal or caulk cracks or crevices that may look inviting to spiders. Wash the outside of your house or building, paying particular attention to areas surrounding the window wells and other undisturbed places where webs are often built. A stiff broom is helpful because spiders are fragile and consequently, easily killed.