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Courtesy of Holistic Pest Management

Brown recluse spiders are often called violin spiders or fiddleback spiders because of the violin-shaped marking on their back. These spiders have a body about 3/8 of an inch in length with a thin abdomen, are light brown in color, and have long, thin legs. The “recluse” in brown recluse spider comes from this spider’s secretive habits. It prefers to spend the day in dark, secure areas and ventures forth only at night to hunt for prey.

Infestations generally involve few spiders, usually less than 15 to 20. Even one brown recluse spider in a building is too many, and control measures are necessary when this spider is detected and positively identified.

It is when the brown recluse decides to rest or hide in between the folds of seldom used clothing, bed sheets and covers, or shoes, that it becomes a danger to people. This spider is not aggressive and will only bite - as a defensive reaction - when it is accidentally trapped against a person’s skin. Bites most often occur when a person puts on a piece of clothing or shoes in which a spider is hiding or when crawling under sheets or covers where a spider rests.

The bite of the brown recluse spider is usually painless although some persons may experience a small sharp pain resembling the sting of an ant. The brown recluse venom is cytotoxic. This type of venom causes tissue death (necrosis) which can result in large ulcerating sores that may take months to heal.

These spiders range in size from 3/8 to 5/8 inches in body length and 5/8 to 1-3/4 inches in leg span. The abdomen usually has a herringbone stripe pattern of brown, grey and tan. Two parallel grey marks run the length of the carapace (back of the head).

These spiders are generally found in the lower rooms or areas of buildings, being found most commonly, but not exclusively, in crawlspaces and basements. The aggressive house spider will build its web in any location that has a hole or cavity in which to build a web. The presence of a hole or crack seems to be necessary before the aggressive house spider can build its web. Also, the webs of this spider will generally be located near the floor as it is a poor climber.

The venom of the aggressive house spider is cytotoxic in nature and produces symptoms that are similar to, and sometimes as equally severe as, those of the brown recluse spider.

Normally, the bite of the aggressive house spider is not felt, nor is the spider seen. Within a short period following the bite - from 15 minutes to an hour - a reddened area develops around the site. In some cases, this redness subsides within a few days and no further tissue involvement is noted. Often, the bite of the aggressive house spider causes far more serious results.

The black widow spider is perhaps the most well-known spider in North America. The adult female is usually jet black above, with a characteristic sphere-shaped abdomen and two reddish triangular markings, joined to form an “hourglass” shape on the underside of the abdomen. Mature females are nearly ½ inch in body length.

The northern widow is black with a row of red spots along the middle, top of the abdomen. The hourglass marking is often broken onto two separate spots. This species is probably the most medically important black widow spider.

Widow spiders are generally nonaggressive and will usually retreat to the corner of their web when disturbed, however, they will be more aggressive when protecting an egg sac. Bites usually occur because someone accidentally traps them against their skin by putting on clothing or shoes in which the spider is hiding.

Black widow spiders most commonly build their webs in secluded, protected sites under dense shrubbery, under boards, in firewood piles, under or inside logs, under furniture, behind and under any debris, inside boxes and even inside seldom worn shoes. The more cluttered the area, the better these spiders like it because clutter provides shelter for the insects they prey upon.

The venom of the widow spiders is neurotoxic. This type of venom causes systemic symptoms with little or no local damage or necrosis. Neurotoxic venom travels via the nervous system and can cause symptoms and reactions at sites far removed from the bite area. Although the black widow’s venom’s main component is more potent than the venom of a pit viper on a volume per volume basis, it is injected in such small quantities that death is rare. The bite of a black widow is most dangerous to small children and elderly persons.

Symptoms of black widow bites may be summarized as follows: The initial bite may go unnoticed or may feel like little more than a pin prick. The initial pain may be followed by a dull, numbing pain in the affected extremity and by pain an cramps in one or several of the large muscle masses - particularly the abdomen. Sweating, weakness and pain in the lymph nodes may occur. Symptoms may progress to a sharp increase in blood pressure (hypertension), nausea, leg cramps, tremors, loss of muscle tone and vomiting. In severe cases, the toxin may cause breathing difficulties, heart irregularities and even death. It should be noted, however, that less than 1% of those bitten by a black widow spider die.


A thorough, professional inspection inside and outside the building is needed to determine the spiders involved, the sources of the infestation, how they are entering, and any contributing conditions. Nonchemical techniques should comprise the majority of the control efforts for most spiders in and around structures.

Sanitation: Removal of spider webs, egg sacs, and potential harborages is critical to long-term success in spider control. Indoors, store boxes off the floor and away from walls to limit their use by spiders. Seal all openings of boxes with tape to prevent spiders use as a harborage.

Removal of all new and old webbing allows for easier determination of future spider activity. Removal or straightening of clutter in storage areas, garages, sheds, basements, or outside eliminates potential web-building sites and is important for the control of brown recluse and black widow spiders.

Exclusion: Keeping spiders from entering is the best strategy for preventing inside activity. As many cracks as possible in exterior walls should be sealed and tightly-fitting screens installed in windows and foundations and attic vents. Tight-fitting weatherstrips should be present around the edges of all doors, especially at the bottom.

Exterior Lighting: Exterior lights on buildings attract insects and, subsequently, spiders. Mercury vapor lights should be replaced with sodium vapor lights which are less attractive to insects. Lights should be mounted away from the building shining on the building from a distance. Outside light fixtures on homes can be equipped with “yellow” light bulbs.

Ventilation: Installation of proper ventilation in crawlspaces and attics reduces excess moisture and, therefore, insects and the spiders that prey on them.

Vacuuming: The use of a vacuum device removes not only the individual spiders but also webbing and egg sacs - all in one procedure. Vacuum devices equipped with several extension tubes are useful in the removal of webs and spiders from high corners, rafters, overhead beams, and otherwise unreachable surfaces. This technique is the primary control technique that should be employed for controlling black widow spiders and other web-building spiders.

Weird Fact: Spiders do not eat their victims, they drink them. Able to take food only by sipping it in liquid form through their tubelike mouths, spiders first cover their victims with a special fluid that causes them to dissolve. They then suck up the dissolved tissue. It is by this means that a tarantula is able to ingest an entire mouse, bones and all, in about a day and a half.

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