Follow the Webs: Identifying Black Widow Spiders

Matthew D. Terry Ph.D., Entomology

Members of the spider genus Latrodectus are commonly called black widow spiders. The females are approximately the size of the tip of your finger and are easily identified by their distinctive, dark black bodies and red, hourglass shaped marking on the ventral side of the abdomen. Male black widow spiders are about one third the size of the females and light brown in color. Like all spiders, black widows are predators and have two fangs on either side of the mouth that function like small hypodermic needles. These fangs are used to inject a small amount of a neurotoxic poison that paralyzes the prey, usually a small beetle, roach, or cricket.

Black widow spiders occur commonly in Arizona’s warm, desert environment and prefer to spin their webs in a cool, sheltered area. These webs are cobweb in form, that is without any clear pattern or shape and are nearly always outdoors. Sometimes a black widow will set up house indoors, particularly if it finds a suitable spot that is not often used like a dark corner of the garage or a storage closet.

Male black widow spiders are harmless, but the venom of a female is highly toxic to humans. Fortunately these spiders produce and inject such minute amounts of venom that serious injury or death due to a black widow bite is extremely rare.

The severity of the reaction depends on:

  • location of the bite
  • amount of venom injected
  • individual sensitivity to the toxin with small children and the elderly being the most vulnerable

Although the victim may feel the bite as it occurs often there is little or no initial pain. Spider bites, including the black widow’s, can be recognized by the presence of two small puncture wounds at the center of the affected area. Symptoms include redness and irritation at the site of the bite, pain traveling from the bite and settling in the abdomen or lower back, and muscle cramping. In extreme cases more serious symptoms such as labored breathing, fever and increased blood pressure may occur. If you are bitten by a black widow spider you should contact your physician or local poison control center and, if possible, capture the spider for positive identification. Although medical intervention often is not needed, a bite from this spider should be treated seriously and victims should seek medical advice.

Most bites occur when the spider in inadvertently threatened or trapped by a hand, foot or other body part. A small amount of care and attention can dramatically reduce the probability of having an unpleasant encounter with a black widow. Because it is impractical to remove all suitable habitation sites, effective integrated pest management including regular application of pesticide products, with special attention to areas that are attractive homes for these spiders will significantly increase the likelihood of maintaining control.

Control Measures

You can reduce the probability of having black widow spiders on your property by removing or reducing areas that provide suitable habitats. Unneeded piles of boxes or storage material in the garage, debris and woodpiles in the back yard, and empty, enclosed spaces under or near the foundation of a house all provide prime habitat for black widow spiders. When working around or reaching into these areas, particularly if spider webs are present, care should be taken to avoid being bitten.

About the author: Matthew Terry is the contributing entomologist for Blue Sky Pest Control. He did his post doctoral work at the University of Arizona and currently continues his research and teaches at the University of Texas in Edinburg. Contact Blue Sky Pest Control at 480-635-8492 if you have additional questions or visit the website at www.www.blueskypest.com.


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