Spider Bites

Dr. Jorge Parada - National Pest Management Association

Harry Potter’s friend, Ron Weasley, is probably in good company when he admits he hates spiders. But how much of spiders’ negative notoriety is really just a bad rap?

In truth, spiders are not intentionally harmful to humans. Most spider bites occur when humans accidentally trap or brush up against a spider and receive a defensive bite. On rare occasions, spiders may have a serious lapse in judgment and bite a human finger (or other body part) mistaking it for a caterpillar or other such prey. Even then, most spiders are too small and not capable of breaking the skin with their fangs, or their venom too weak to be dangerous to humans. Simply put — most spider bites are accidental, harmless and require no specific treatment.

Still, that is not enough to stop spiders from having a bad reputation. It is common for any unexplained skin irritation to be called a "spider bite." In fact, most skin lesions and symptoms that are attributed to spiders are rarely actually due to a spider bite. Research has shown that 80 percent of presumed spider bites are actually bites from other insects, or due to skin infections such as MRSA (a resistant staph infection).

Yet, occasionally, a spider’s bites will cause real harm. Spider bites may cause injury by three mechanisms. First, especially with larger spiders, the bite itself may be painful and cause injury. However, far more concerning is the spider's venom, which can include necrotic agents or neurotoxins. Spider bites rarely transmit infectious diseases.

Most spider bites are less painful than a bee sting. Pain from non-venomous spider bites typically lasts for five to 60 minutes while pain from venomous spider bites frequently lasts for longer than 24 hours. The rate of a bacterial infection due to a spider bite is low (less than one percent). 

The two spiders of greatest concern in the United States are the brown recluse and the black widow spiders, most commonly found in southern states. Both species prefer warm climates and dark, dry places. Typically, these are timid, non-aggressive spiders, often found in dry, littered, undisturbed areas such as closets, woodpiles and under sinks.

Black Widow Spiders

Black widow spiders can be found throughout North America, but are most common in the southern and western areas of the United States. Male widows, like most spider species, are much smaller and generally less dangerous than the females. Widows tend to be non-aggressive, but will bite if the web is disturbed and the spider feels threatened. The more dangerous female is a dark colored spider and with a red hourglass marking on its belly. The bite feels like a pinprick, and at first may go unnoticed or seem rather minor. Early on there may be slight swelling and faint red marks. Within a few hours, though, intense pain and stiffness begin. Other signs and symptoms include: chills, fever, muscle cramps, and gastrointestinal symptoms such as nausea, vomiting and severe abdominal pain. Typically, black widow bites are less common, but more severe than brown recluse bites. That said, no one in the United States has died from a black widow spider bite in more than 10 years.

Brown Recluse Spiders

The brown recluse spider, also known as the violin spider, is most commonly found in the south-central, mid-western and southern states of the United States. Most encounters with this spider occur from moving boxes or rooting about in closets, attics, garages or under beds where they may have nested. These spiders are brown in color with a characteristic dark violin-shaped (or fiddle-shaped) marking on its head. Whereas most spiders have eight eyes, brown recluses have six equal-sized eyes. The bite produces a mild stinging, followed by local redness and intense pain within eight hours. A fluid-filled blister forms at the site and then sloughs off to leave a deep, enlarging ulcer. Systemic (or generalized) reactions from a brown recluse spider bite vary from a mild fever and rash to nausea and listlessness. Generally, brown recluse spider bites are reported much more frequently than black widow bites, but while the brown recluse bite may cause very significant local skin reactions, it is much more unusual for these bites to cause generalized symptoms. Unfortunately, brown recluses are almost communal and can be sometimes be found in great numbers.

What To Do

• If you suspect a spider has bitten you, try to bring it with you to the doctor so they can determine the best course of treatment based on the species.
• Clean the site of the spider bite well with soap and water.
• Apply a cool compress over the spider bite location (using a cloth dampened with cold water or filled with ice).
• If you suspect the bite is form a black widow or brown recluse spider, and the bite is on an extremity, elevate it.
• Consider tying a snug bandage above the bite and elevate the limb to help slow or halt the venom's spread. Ensure that the bandage is not so tight that it cuts off circulation in your arm or leg.
• Adults can take aspirin or acetaminophen and antihistamines to relieve minor signs and symptoms (but use caution when giving aspirin to children or teenagers).
• Seek medical attention for any severe signs and symptoms, or if signs and symptoms continue to worsen for more than 24 hours.

When To Worry

If a local reaction continues to get worse for more than 24 hours, it may be time to seek medical attention. Look for redness spreading away from the bite, drainage from the bite, increase in pain, numbness/tingling, or a discoloration around the bite that looks like a halo or bull’s-eye. If generalized symptoms set in, be concerned. In very rare cases, there have been reports of spider bites (by spiders considered otherwise harmless) causing allergic reactions - including anaphylactic shock, a life-threatening condition (much like may result from the sting of a bee, or wasp in a highly allergic person).

Contact a pest professional if you think you may be dealing with a spider infestation.