University of Missouri Extension

Chuck Adamson
Senior Information Specialist
573-882-6843
adamsoncw@missouri.edu

Published: Aug. 10, 2006
Story Source: Richard Houseman, 573-882-7181

Brown recluse common in Missouri
but less likely in clutter-free homes

COLUMBIA, Mo. - The site of a brown recluse spider can evoke fear and conjure up images of ulcerated wounds brought on by their venomous bites.

While bites in some cases can cause wounds and caution is warranted, the spiders are rarely aggressive and most bites result in just minor to moderate skin irritations, said Richard Houseman, University of Missouri Extension urban entomologist.

"I think it is a serious thing to worry about, but only 2 to 3 percent of bites cause a skin reaction bigger than the point of a pencil. People worry that if they get a bite they're going to lose their arm," Houseman said. "Most people have (brown recluse spiders) in their home, especially when they have lived in a house for a while."

Houseman recommends simple steps to keep the spiders from coming in contact with people.

To begin with, he said, accurately identify the spiders. Many beneficial spiders - ones that prey on other spiders and insects but are themselves harmless - often are mistaken for the brown recluse by non-experts. The most distinguishing feature of the brown recluse is the dark violin marking on the top portion of its body. The neck portion of the violin points toward the spider's bulbous abdomen.

The spiders are about 3/8 inches long and 3/16 inches wide.

Brown recluse spiders have six eyes, set in three pairs. Most other spider species have eight eyes.

The spider's behavior is true to its name.

"Brown recluse are extremely secretive and often are hard to spot," Houseman said. "They like to hide in places where they are unlikely to be found."

Clutter becomes harborage spots for the spiders; lots of clutter left undisturbed for long periods in a home can be magnets for the spiders and cause major infestations, he said.

Some common places the spiders are found include: inside shoes; within dressers; in showers and tubs; underneath couches and other pieces of furniture; in stacks of clothes; in bed sheets of beds that are rarely used; behind baseboards and pictures; and in boxes.

An MU-based study done in the 1970s concluded that about 80 percent of Missouri homes harbored brown recluse spiders. Some homes can have thousands with residents never suffering a bite.

The spiders cannot bite a human unless pressure is applied to the spider and against the victim's skin. Pain can be immediate from a bite, but often a person won't know they have been bitten for an hour or more. Stinging is usually the first symptom, followed by intense pain. A small white blister will appear. The area will swell, become hard to the touch and eventually tissue may die, leaving an ulcerated sore the size of a dime or less. In extreme cases the wound can grow very large, a couple inches or more in diameter. Fatalities are rare.

A person who suspects they have been bitten should obtain medical attention immediately. There is no anti-venom commercially available, but doctors often treat the sores in various ways.

Some tips to keep from being bitten include:

  • Shake out and inspect gloves, shoes and boots before putting them on.
  • Wear gloves when cleaning out cluttered areas where spiders may harbor. Also, wear gloves when handling firewood, lumber and rocks.
  • Shake out clothing before putting it on.
  • Inspect bedding and towels before use.
  • Remove bed skirts and storage boxes from underneath beds. They are bridges of access for spiders to enter a bed. Also, move beds away from walls where spiders can access the bed.
  • Watch for spiders when handling cardboard boxes.

To monitor for the spiders, Houseman suggests using bug sticky traps, which are available at home improvement stores. Place them in out-of-site areas where the spiders like to hide, such as under furniture. In the case of major infestations, Houseman recommends hiring a professional exterminator with experience in treating for brown recluse spiders.

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