How to Detect and Treat Spider Bites

July 08, 2016

Lisa Esposito

U.S. News & World Report

Spiders can cause minor skin irritations or toxic reactions.

You're just sitting there, minding your own business, and along comes a spider, sinking its fangs into your skin. Most spider bites are harmless, but a few can do serious damage. Culprits – from common house spiders to venomous black widows and brown recluses – can lurk at the lake house, nip from a bag of grapes, creep out of a gym locker or hide in a hoarder's pile. If you think you have a spider bite, here's what to know and do.

Was That a Spider?

Often, people aren't aware of insect bites at zero hour but later notice a small bump or red spot. If the bite is itchy rather than painful, it's more likely a mosquito bite than a spider bite, says Dr. Amy Kassouf, a dermatologist at Cleveland Clinic.

"Spiders can often itch or hurt," Kassouf says. "Spider bites tend to swell a little bit more over a longer period of time." Not as smooth, spider bites tend to have a central puncture area – fang marks – where the stinger was inserted. Bites from more venomous spiders tend to hurt and swell more, she says.

Indoors, you can find spiders under eaves, in your attic or in dusty, neglected areas. Outdoors, anything by the water attracts spiders. "Lake houses tend to have lots of spiders," Kassouf says. Spiders like spinning webs in areas with plenty of bugs, she adds, so watch out for those nooks and crannies.

If you see the spider that bit you, taking it with you as you seek medical care could be helpful for guiding treatment. But that rarely happens among his patients, says Dr. Andrew Murphy, an asthma and immunology specialist at Asthma, Allergy & Sinus Center in West Chester, Pennsylvania. "In 20 years, I've never had someone bring in a spider for me," he says.

[See: How to Avoid Summer Pest Risks – From West Nile to Chikungunya Virus.]

First Aid for Minor Bites

If you are bitten by a spider, wash the site with soap and water. A cool compress can ease swelling, and an over-the-counter pain medicine such as Advil, Aleve or Tylenol can relieve pain.

Most bites just go away, Kassouf says. If itching and discomfort persist, topical steroid creams can help, she says. If bite discomfort keeps you up at night, she says, oral antihistamines or prescription steroid pills are options.

Murphy tends to tell patients to use Allegra, Zyrtec or Claritin for itchy bites because they're less sedating than Benadryl. He also advises against topical Benadryl or other antihistamine creams, which can make rashes worse.

"If you scratch a lot and you open [the skin] up, then you might need a topical antibiotic so it doesn't get infected," Kassouf says. Scratching opens the door to staph and other infections. "That's the main reason you don't want to scratch too much," she says.

Young children with suspected spider bites should be seen by a doctor.

With bites on the head or neck, the biggest initial concern is swelling, Kassouf says. Significant swelling from an an allergic or inflammatory reaction could potentially compromise the airway or other functions of vital structures of the face, she explained in an email. "Since some spider bites (like the brown recluse) can cause necrosis (tissue death), this is much more serious and hard to treat surgically on the face, head and neck," she wrote.

[See: Is It Healthy to Sleep With Your Pets?]

Venomous Spiders

Black widows. With their shiny bodies, long legs and red hourglass markings, black widow spiders are easy to identify. "But their bites are very, very painful," Murphy says. Kids have been bitten in gym locker rooms, he says, as the spiders are attracted to dark, moist areas. Woodpiles are also favorite haunts.

At first, skin around a bite swells at the site, and you may notice one or two fang marks along with burning, swelling and redness. Later, pain spreads, eventually reaching your back and belly. You could experience severe cramping or rigidity in your abdominal muscles.

Other symptoms can include heavy sweating, nausea, tremors, difficulty breathing, fever, restlessness and a rise in blood pressure. Pain usually lasts up to 12 hours, with symptoms possibly persisting for several days.

If you suspect you've been bitten by a venomous spider, wash the bite and elevate the area to keep venom from spreading. Call Poison Control at 800-222-1222 for advice. You may be told to seek immediate emergency care. Treatment can include anti-venom for black widow spider bites, pain medicine, muscles relaxants, steroids, antibiotics and a tetanus booster shot, depending on your symptoms.

Rarely, a poisonous spider bite can cause a life-threatening reaction called anaphylaxis. "If you start getting hives, lip swelling, tongue swelling, short of breath, wheezing, light-headed, dizzy – obviously, that's a bad thing," Murphy says. Call 911 for this medical emergency.

Brown recluses. Brown recluse spiders are known for the striking violin pattern on their backs and their rare but dangerous bites. They're primarily seen in Southeastern and Midwestern states, but are occasionally spotted elsewhere. The spiders are, well, reclusive rather than aggressive, usually biting only when threatened and next to someone's skin.

Some bites may be painless or have a slight burning feel at first. A small blister may form. A few hours later, severe pain and itching can develop, along with nausea and vomiting, fever and muscle pains.

Even in small quantities, brown recluse venom is toxic and destructive. Enzymes in the venom attack nearby cells and destroy skin, fat and blood vessels around the bite, leading to necrosis. With necrosis, Kassouf says, the bite area usually turns dark purple to black in the center, and it starts to look more like a scab or deep bruise.

As the body's immune system responds to toxins, severe side effects could include red blood cell destruction, blood-clotting problems, acute kidney damage and death. Deaths from brown recluse bites are rare and occur most often in small children.

In some cases, skin and cartilage damage can be severe, necessitating surgery and leaving permanent scars and other lifelong aftereffects. Emergency treatment is similar to that for a black widow spider bite to stem the body's reaction, treat complications and prevent prolonged health damage.

[See: 10 Seemingly Innocent Symptoms You Shouldn't Ignore.]

Shaking Off Spiders

The National Capital Poison Center website offers steps to lower spider-bite risks, such as shaking gloves, boots, shoes, clothing and blankets out before use, especially if they've been in storage.

Before entering basements, attics, unused closets and storage areas, make noise or vibrations. Cut clutter to eliminate nooks and crannies. Consider glue traps for your home, and contact a professional pest control operator if you suspect an infestation.

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