Artificial spiders, especially replicas of the venomous black widow, tend to pop up all over the place at Halloween. Plastic models of the black arachnid with the telltale red hourglass marking on its abdomen suddenly appear at schools, malls, and office places. But, as I learned this summer, black widows aren't just a Halloween decoration.
While working on a biology survey in a park in the Boston suburbs I was poking around a rocky ledge when suddenly I caught a glimpse of an inch-long black spider with bright red markings on its large, round abdomen. A black widow? In Massachusetts!? I'd seen many black widows in the southwestern United States; but, I'd never seen one on the East Coast, and I didn't even know they occurred in Massachusetts.
I snapped a few photos which I later sent to a local spider expert. He confirmed it was in fact a black widow, the northern black widow, Latrodectus variolus, to be specific. Unlike the southern black widow, Latrodectus mactans, which has a complete red hourglass marking on the underside of its abdomen, in the northern black widow the two halves of the hourglass marking are not connected. The northern black widow also has a row of red spots along the middle of its back. The northern black widow can be found from northern Florida to southeastern Canada, while its southern cousin typically is found only as far north as New York. A third black widow species, Latrodectus hesperus, is found in the western United States.
Like many other spiders, black widows construct webs that they use to trap the insects and other arthropods they feed on. Shy, secretive, and nocturnal, black widows usually build their webs in places like wood piles or under rocks. They can also be found in sheds and garages, and may move indoors into basements and crawl spaces when the weather turns cold.
Black widows are the most venomous spiders in the U.S. Named for their alleged tendency to kill and eat the smaller, brown colored males after mating (which, in reality, rarely occurs) only female black widows pose a danger to humans. Although their venom is highly toxic, they inject such a small amount it is rarely fatal.
The venom is a neurotoxin, which means it affects the nervous system. The bite itself has been described as being like a pin prick. Sometimes a person may not even know they've been bitten. There can be local swelling around the area of the bite, as well as two red spots where the spider's fangs have penetrated the skin. Pain spreads from the site of the bite and settles in the abdomen and back. Severe cramping can occur in the muscles of the abdomen, back, chest, and shoulders. Nausea, vomiting, sweating, tremors, swelling of the eyelids, difficulty breathing, restlessness, and an increase in blood pressure can also occur.
If you think you've been bitten by a black widow stay calm and contact your doctor, local hospital, or regional poison control center (1-800-222-1222 in Massachusetts) for help. An ice pack applied to the area of the bite can help relieve pain and swelling. If possible, collect the spider in a jar or plastic bag so it can be identified later.
Medications such as calcium gluconate can be given by a doctor at the hospital to help control pain, and an antivenin is also available to help counteract the spider's venom if the severity of the symptoms warrants it. Symptoms tend to diminish after about a day, and resolve completely within a few days. Deaths and long term complications are rare. According to the Boston Children's Hospital Web site, less than three deaths per year occur from spider bites in the United States, most of these in young children.
Black widows are not common in Massachusetts, so they're not likely to be a problem. Wearing long sleeved shirts and gloves when working around the yard or moving firewood or lumber can help prevent spider bites, as can shaking out shoes or clothing before getting dressed. Keeping your home and yard clean and free of clutter where black widows might naturally tend to hide can help keep them out as well. If you think you've seen some in your home it's best to contact a professional pest control specialist to deal with them.
It's also important to remember that spiders, including black widows, play an important role in the environment by eating insects such as flies and mosquitoes we commonly regard as pests, and that most spiders pose no threat to humans.
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Don Lyman is a biologist and pharmacist, and teaches as an adjunct instructor in the Biology Department at Merrimack College in North Andover.
