All Sorts of Stings: Venemous Spiders

When I was in college, my apartment was infested with hobo spiders. At one point, my wife and I were catching three or four spiders every night. We probably could have found more, but their coloring blended in perfectly with our carpet– not a very comforting fact. By all standards the little guys seemed to be looking for a fight; at least I believed so when one stared me down from across our living room and then charged.

Ever since then, I’ve been plagued by simultaneous disgust and fascination with spiders. They’re incredibly interesting bugs, but I can hardly stand looking at them.

All spiders are venomous, but North America is home to only three species that are considered a threat to humans. Most spiders either have venom too weak to be harmful, or teeth too small to puncture human skin. Contrary to a popular myth, “daddy long legs” spiders are not one of the most venomous species in North America. That distinction belongs exclusively to the black widow.

Widows

Despite her small size, the female black widow spider is the most venomous creature in North America. Her tiny droplets of poison put both rattlesnakes and scorpions to shame. Male and juvenile widows, however, pose no threat to humans.

Female black widows are easy to recognize from their shiny black, globular bodies and the distinctive red hourglass shape on their underside. The spiders are primarily nocturnal, preferring to hide during daylight hours. Black widows build haphazard, tangled webs of impressively strong silk. If you ever walk through a black widow’s web, you will probably feel the tension in the strands, and notice an audible tearing sound as they break.

In nature, black widows build their webs on rocky outcroppings, under logs, and between stones. Amidst human habitation, they prefer outbuildings and undisturbed clutter.

Black widows aren’t considered aggressive (meaning they won’t come looking for a chance to bite). Typically, they mind their own business and bite only upon accidental contact with a human. This occurs most frequently when someone reaches under an object where a spider is hiding, or when the spider becomes trapped in clothing, gloves, or shoes.

Black widow venom contains potent neurotoxins that spread through the lymphatic system. Patients rarely feel the bite, but some report instant, sharp pain.

Initially there might not be any redness or swelling around the bite, but later a small red bump may appear. Symptoms of the bite are systemic, and usually start to show up 1 to 3 hours later. Victims usually experience severe pain, muscle cramping, and intense anxiety. Abdominal and back muscles usually become rigid and board-like. The victim sometimes experiences a burning sensation or numbness in the feet. Other common symptoms include headache, nausea, vomiting, dizziness, and heavy sweating.

Even though the symptoms are traumatic and patients often feel a sense of impending death, black widows kill very few humans. Usually their bites are only deadly to very small children, the elderly, or those who have an allergic reaction to the venom.

The best thing you can do for someone who has been bitten by a black widow spider is provide calm reassurance. If you can locate the bite, wash it and cool the injury. Unlike snake bites, it’s acceptable and sometimes beneficial to apply ice. The cold may help reduce the pain, as well as the spread of the venom.

Get the victim to a hospital, since complications can arise. Antivenin is available for black widow bites, but it’s rarely necessary.

Recluses

Brown recluse spiders vary in color from light brown to a reddish hue. In adults, the body is usually about a centimeter long. A darkened patch resembling the shape of a violin marks the top front body segment (right behind the eyes). Not all recluses exhibit this feature, though.

Nesting populations of brown recluses only live in the South and the southern Midwest. In the wild they hide beneath rocks, bark, and leafy plants. Unlike black widows, recluses are comfortable living in close proximity to humans. They can often be found indoors in dark corners, draperies, and closets. Brown recluse spiders usually bite upon accidental contact with the skin, such as when they become trapped in clothing or bedding.

The bite of a brown recluse is often painless. Many people don’t realize they’ve been bitten until after the fact. Anywhere between 1 and 5 hours later, a blister usually forms at the puncture site. The classic “bull’s-eye” lesion of a recluse bite consists of a red, aggravated blister surrounded by a bluish circle, which is in turn surrounded by another red circle. The victim may sometimes experience a fever, chills, or weakness.

Often the injury resulting from a brown recluse bite will form a scab and gradually heal over a period of 1-2 weeks. Sometimes, the venom eats into subcutaneous fat and forms a necrotic ulcer that takes months to resolve. In a few individuals, recluse bites have resulted in systemic complications or death.

Clean the bite with antiseptic if possible, and apply cold to help reduce the pain. Crater-like skin ulcers should be examined by a professional as soon as possible.

Hobos

Hobos are light tan in color with a brown or grey herringbone pattern on the top of the abdomen. Their bodies are usually 0.5 – 1.5 centimeters long, with a leg span of 1.25 – 3.75 centimeters. Hobo spiders are native to Europe. They probably arrived in the United States as stowaways on shipping vessels arriving in Seattle. They now populate much of the Northwest. Their range currently extends east to Montana and south to Utah and Oregon.

Like brown recluses, hobos tend to hide during the day and roam nocturnally. Outdoors they can be found hiding under rocks, woodpiles, and other debris. Indoors they seek out undisturbed dark corners, cupboards, and furniture.

Unlike recluses and widows, hobo spiders sometimes behave aggressively. They usually bite when trapped in clothing or bed sheets, but sometimes they bite with little provocation.

Hobo bites typically form a blister followed by a skin ulcer that takes several months to heal. Hobo bites may cause necrotic lesions like the brown recluse, but they’re usually less severe. About half of all patients experience symptoms such as severe headache, disorientation, weakness, and/or visual abnormalities. When administering first aid, clean the bite with antiseptic and apply cold. Painkillers can be given to help alleviate discomfort.

Prevention

Check clothing, boots, and gloves for spiders before putting them on. If you’re camping in spider habitat, keep the tent zipped up. Wear shoes when walking around the campsite at night. Most importantly, watch where you put your hands, and don’t try to catch spiders.

Spider bites are often difficult to diagnose unless the offending arachnid was caught in the act and captured for identification. There isn’t much that can be done to treat a bite. If you are bitten, don’t panic. Fatalities are extremely rare. Up to 50% of spider bites are thought to be dry, meaning no venom is injected.