Brown recluse spiders are one of the few species of spider that pose a potential threat to humans.

There are more than 3,500 known species of spider in the United States. Although spiders cause fear in many people, only about five main groups worldwide can potentially cause significant reactions in humans.

In the U. S., these venomous species fall into two different groups: Brown spiders and widow spiders.

Brown recluse spiders belong to the brown spider group. The other well-known venomous spider is the black widow spider, which falls into the widow group.

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Brown recluse spiders are highly venomous, but can only release small amounts of venom at a time.

The brown recluse spider is also known as the violin or fiddle-back spider. It lives in midwestern and southeastern parts of the U.S. This spider is brown and has a darker, violin-shaped spot on its back.

Unlike other spiders, which typically have eight eyes, brown recluse spiders only have six, arranged in three pairs of two eyes each. The legs of a brown recluse are long, thin, and covered in small hairs. The scientific name for this spider is Loxosceles reclusa, which can be translated from Greek as "with slanted legs."

These spiders are most active at night and rest during the day, hidden away in dark areas. If they come indoors, brown recluse spiders prefer closets, attics, basements, and other dark areas of the house. They seem to prefer dry areas.

The venom of a brown recluse can be highly toxic, but the spiders are only able to release a small amount during a bite. People are also more likely to come into contact with the male spider, which has only half as much venom per bite as a female spider.

Why do they bite humans?

Brown recluse spiders only rarely bite humans and do so out of self-defense. They are not aggressive towards humans and prefer running away to biting.

Bites occur when the spider gets trapped against the skin, such as in tangled bedsheets or in clothing and shoes.

It is important to check and shake out linen and clothes before using them when living in an area to which these spiders are common, especially if they have not been in recent use.

There are many myths about brown recluse spider bites.

One common myth is that their bite always causes severe wounds and destroys skin tissue. In reality, only a small number of bites result in this type of injury. Most bites either cause no symptoms at all or only mild reactions.

Extremely rare complications can occur across the entire body, including acute anemia, blood clotting problems, and kidney failure.

The bite is usually painless to begin with, and occasionally symptoms will progress with time. Most bites occur on the thigh, upper arm, and chest.

If a skin reaction is to occur, over the first hour a person may experience the following symptoms around the area of the bite:

  • redness
  • swelling
  • a burning sensation

Over the next 2 to 6 hours, the site of the bite gets bigger, becomes more painful and forms a blister. if the area around the bite becomes more purple in color around 12 to 24 hours after the bite, skin death will likely occur. This is known as necrosis. If necrosis occurs, it can take several weeks or even months for the wound to heal fully.

However, according to spider experts at the University of Florida, if there are no signs of skin changes within 48 to 96 hours, the wound will not become necrotic and should heal properly.

While these spiders do not often bite humans, they pose a slightly higher risk to people who work indoors.

Machinists, janitors, and housekeepers might face an even higher risk, due to working in areas where there is an increased likelihood of coming into contact with the spiders.

Living in the Midwest or the southeastern U.S. is the main risk for accidental encounters with this type of spider.

Complications

Despite their fearsome reputation, only about 10 percent of brown recluse spider bites lead to serious skin complications.

There are no documented cases of death as a result of a brown recluse spider bite.

What people call spider bites are often misdiagnosed, usually the result of other skin conditions or infections.

Tick bites, viral, fungal and bacterial infections, drug reactions, and skin complications from diabetes are common causes of similar-looking skin reactions.

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Clean a brown recluse spider bite with water and mild soap as soon as it happens.

People can typically treat real spider bites at home. If possible, people should collect and identify the spider responsible.

Do this by trapping the spider under a clear cup or jar so the spider can be easily seen, and slowly sliding a piece paper under the container. Turn the container over and secure the paper over the top or attach a lid.

If someone receives a bite, they should clean the wound with mild soap and water.

If the bite is causing discomfort, elevate it if possible and apply a cool compress or a covered ice pack to reduce swelling and pain.

A pain reliever, such as acetaminophen or ibuprofen, can be helpful in reducing discomfort. An antihistamine, such as Benadryl, may also help with any itching.

People should see a doctor for any wound that is painful, red, oozing, or not healing properly.

If a brown recluse spider is confirmed as the cause, the doctor may recommend a tetanus booster if a person has not received one in the last 5 years. The doctor may also want to check the wound in 2 to 3 days after the bite, to ensure that the venom is not destroying tissue. Treatment can commence quickly if there are any concerns. This reduces the risk of further complications.

Diagnosis

There are many other conditions that can cause a severe wound similar to brown recluse spider bites. These conditions include tick bites, infections from bacteria, viruses and fungi, diabetes, and other skin conditions.

Unless a person lives in an area where brown recluse spiders are known to live and has caught the spider for proper identification, the cause of a wound should not be blamed on a brown recluse spider bite.

A person with a brown recluse spider bite has an excellent chance of recovery, especially with proper care, since most bites require no particular treatment and heal on their own.

In most cases, minor wounds from these types of bites heal completely within a week or so.

People with other medical conditions, such as diabetes or immune system problems, are at a higher risk of complications. These individuals are also at higher risk for a wide variety of skin infections and other skin problems. However, it is especially important for them to contact their doctor in the event of an actual or suspected brown recluse spider bite within 24 hours if there is a reaction. Any wound that is not healing properly needs to be evaluated, regardless of the cause.

Though brown recluse spider bites are rare, it is possible to reduce the risk of getting one. These steps are important for people living in the areas where brown recluse spiders settle.

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Outdoor wood piles can attract brown recluse spiders.

The best way to do this is by avoiding areas where brown recluse spiders tend to live, such as dry areas with outdoor wood or rock piles. Someone who works near or in these areas should wear gloves.

When indoors, people should be sure to shake out clothing, shoes or bedding that they have not used for a while, particularly if they are kept in an attic, basement, or dark closet.

Taking other measures to prevent brown recluse spiders from setting up home can be useful. Cleaning out attics, sheds, closets, and basements gets rid of the spiders' preferred hiding places. However, it's important to remember, a brown recluse spider would rather escape from you than bite you.

Removing outdoor woodpiles can prevent their accumulation in these areas.

Even though these spiders have gotten a bad name, the actual risk of significant injury from a brown recluse is quite small.

Simple preventive measures can be highly effective, further reducing any risk of encountering these spiders.

Q:

What should I do directly after a brown recluse spider bite?

A:

Since most brown recluse spider bites result in either no symptoms or only a mild reaction, washing the bite with warm soapy water and patting it dry with a clean cloth is the first step.

Any reaction within a week of the bite that includes fever, chills, rash, yellowing of the skin, paleness, fatigue, dizziness, or vomiting requires immediate medical attention.

If a skin reaction is going to occur, changes should be seen within a few hours. This includes increased size, redness, pain, and usually blisters. Within a day the wound may become purple. This is often a sign that skin death, or necrosis, will occur.

It is important to see your doctor if these types of skin changes happen so that you can receive any appropriate vaccinations, medications, or wound care. You will likely need close follow-up to make sure the wound heals properly.

Judith Marcin, MD Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.