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Spider Bites: Real or Imagined?

January 27, 2010

I would like to pass this along to you, from the National Pest Management Association.

Brown Recluse Spider Bites – Real or Imagined?

The number of reported brown recluse spider bites has increased dramatically over the past few years. In addition, the geographic locations of the reports suggest two possible explanations: Either the brown recluse spider's range is increasing dramatically, or the bites are being misdiagnosed. The latter is the more likely scenario.

The brown recluse spider, Loxosceles reclusa, has gained a reputation over the years as one of North America's “medically important” spiders. Although the brown recluse's natural territory range in the United States is in the southern states, primarily from western Georgia through Texas, it has been known to range as far north as parts of Missouri, Indiana, Illinois and Nebraska. However, bites from this species have been reported throughout the country. States in which reported brown recluse bites have occurred include Maine, Minnesota, New Jersey, Delaware, Maryland and numerous other northern locales. While the reclusive nature of this spider may enable it to be transported from its natural habitat to other areas, it is unlikely that the brown recluse is responsible for many of the alleged bites that have been reported.

Numerous calls received primarily from pest management professionals indicate that one of their customers, potential customers, or an acquaintance has been bitten by a brown recluse spider. These calls have come from various parts of the United States, including many areas where the brown recluse is not known to occur. The following scenario is typical: The person develops a red blister on their arm, leg or another part of the body; the blister bursts and an open ulcer-like sore develops. When the person goes to the doctor, the doctor looks at the sore and almost immediately diagnoses it as a brown recluse spider bite. In most cases, there was no spider seen, let alone captured and identified. The determination had been made based upon the look of the sore or area of the wound.

In an effort to obtain the most up-to-date information regarding the diagnosis of spider bites, the world wide web was employed. Using the Internet, arachnologists were contacted throughout the United States, the United Kingdom, Europe, and as far away as Australia and Slovenia. Without exception, they reported that it is virtually impossible for a physician to examine a bite and determine, in the absence of an actual specimen, that it was the result of a brown recluse spider. Most also agreed that it is impossible to conclude that the bite was even from a spider.

Alternately known as the fiddleback or violin spider, the brown recluse can inflict a bite that may not even be felt yet may result in severe skin and tissue damage. The bite may be painless, or it may be of the same degree as the sting of an ant. Usually a localized burning sensation develops and lasts about 30 to 60 minutes. Over the next eight hours the reddened area enlarges and a pus-filled blister forms in its center. Within 12 to 24 hours after the bite, systemic reaction may occur, characterized by fever, malaise, stomach cramps, nausea and vomiting. The venom usually kills the affected tissue and causes skin loss and necrosis or death of the underlying tissue. Ulceration develops and a well-defined eschar, or pock-like area, forms. This may take a week to develop. If the bite progresses to this stage, removal of the dead tissue may be necessary followed by skin grafting. Normally the site heals itself in six to eight weeks. In advanced or severe cases, additional symptoms may include jaundice, spleen enlargement, hemolysis, renal failure, and even death, though this is rare. Such extreme symptoms are normally limited to those individuals who possess other medical maladies such as diabetes.

What, then, caused the painful sores or wounds reported if not the brown recluse spider? There may be any number of explanations. Results of a survey by Russell (1991) showed that 80% of suspected spider bites were actually fleas, ticks, kissing bugs, mites, bedbugs, flies, bees or wasps. Several diseases show lesions similar to those produced by bites of brown recluse or other spiders with cytotoxic venom. These may include chronic or infected herpes simplex, arthritis dermatitis, diabetic ulcer, bedsores, poison ivy, and even Lyme disease.

While virtually all spiders are "poisonous" in that they possess poison glands and fangs with which they disable prey, they seldom pose a serious health threat to humans. There are three reasons for this:

The venom of most spiders is not potent enough to cause any severe reaction in the average person.

Most spiders possess chelicerae, or fangs, that are too small to puncture the skin. Of just over 3,000 species of spiders in the United States, only about 50 are capable of biting humans.

Spiders tend to bite people only as a means of defense. They do not view us as a tasty morsel upon which to feed; we are merely a substrate over which they walk. They bite as a means of self-defense. When we put on our shoe or shirt, stick our hand in a box, or roll over one in our sleep, the spider has two choices — fight or flee. Given the opportunity, it will usually choose to flee; however, if pinned, pinched or in any way restricted, it will fight — and in this case, bite.

This is not to imply that physicians may not, in fact, be correct on occasion in their diagnoses. It does mean, however, that they may often be too quick to assume that an open sore and other accompanying symptoms are the result of a bite from a brown recluse spider. Vest (1987) determined that many of the bites in the Northwest were actually from the aggressive house spider (now called the hobo spider), Tegenaria agrestis. Unlike the venom of the black widow spider, Latrodectus mactans, which is neurotoxic, the venom of both the brown recluse and the aggressive house spider causes localized tissue death at the site of the bite.

Cytotoxic venom is also possessed by another common family of spiders: the sac spiders (Family Clubionidae). As indicated by Wegner (1991), sac spiders have reportedly been responsible for inflicting a good number of bites. Active hunters, sac spiders build no webs, although they do construct a small silken sac or tube in which they rest and in which the female places its egg sac. Often this sac may be found at the juncture of the wall and ceiling or behind pictures, baseboards, or any other object that provides some protection. This may also include bed frames, headboards and nightstands. Most active at night, their wandering occasionally brings them into contact with humans. In search of prey, they may find themselves traveling across a bed and even through clothes. When a person rolls over one, he or she may be bitten. This concurs with the fact that the great majority of "spider bites" are noticed in the morning when we awaken.

When someone suspects a spider bite, they should seek medical attention. The area should be cleansed immediately and attempts to locate the spider for proper identification should be made. Remember, it is more likely that something other than a spider is responsible for the bite or reaction. This does not mean that someone can't be bitten by a spider, it only means that it is a relatively uncommon occurrence.

Although the brown recluse does inflict its deadly bite upon numerous people each year, it is far more likely that something else is responsible for the "bite" symptoms that most people experience. These may be from other spiders, other arthropods, or even from something non-living such as a metal, wood or glass sliver that has resulted in severe secondary infection.

The question may arise, "What difference does it make whether the symptoms or sore are from a brown recluse or any other spider, arthropod or even something non-living?" The treatment, after all, is often the same. In the case of a positively identified brown recluse bite, however, early treatment is of great value. Excision of the site is done with less frequency while use of a nitroglycerine patch within the first 6 hours has shown promise.

General treatment of bites or open sores includes cleansing the wound area with iodine or hydrogen peroxide and then topical application of corticosteroids such as prednisone, hydrozine hydrochloride, or phentolamine to promote lesion healing. Dexamethasone, colchicine and dapsone have all been used with some success when systemic symptoms appear. In addition, antibiotics are often administered to prevent bacterial infection at the bite site. Antihistamines are often prescribed as well, although their value is questioned.

Should it really matter, then, whether the sore and accompanying symptoms are from a brown recluse spider or any other spider? In fact it should, because of another way that spiders affect our health. This is what we may refer to as the "fear factor," also known as arachnophobia. Spiders are one of the two most feared creatures on the face of the earth. Along with snakes, spiders evoke fear in an extremely large portion of the population. The thought of having been bitten by a spider can create such anxiety in many people that they can develop additional symptoms. Such symptoms may include nausea and dizziness. The fear may be sufficient to result in changes in normal body functions and chemical balances. To be told that one has been bitten by a spider often causes concern. To be told that one has been bitten by one of the most poisonous spiders in the United States could understandably result in fear, trauma, and anxiety. When this occurs, symptom severity may be increased and recovery may take longer.

In summary, the following points should be reiterated:

Though the brown recluse spider, by its reclusive nature, may be and probably has been transported to many parts of the country, it has not been positively identified in most states beyond its normal habitat range. This is not to say it isn't there, only that it hasn't been identified there by a qualified arachnologist.

Many other arthropods, and even medical conditions, may produce sores, welts and ulcers similar to those of the brown recluse.

It is currently impossible to positively identify a wound as having been inflicted by a brown recluse spider by examining only the wound. The spider should be captured for positive identification.

Speculative identification based solely on symptoms should be avoided to prevent undue concern and resultant secondary symptoms. The patient should be told that the sore or wound may be the result of a spider bite and possibly even a brown recluse. They should also be told that this is highly unlikely, but no chances should be taken in treatment.

Finally, with all of the concern about the venomous bites of spiders, it should be mentioned that some of the components of spider venom may someday save, prolong or increase the quality of our lives. Research has shown, for example, that venom may prevent brain damage in stroke victims if it is administered shortly after the stroke occurs. There is also preliminary research being conducted to investigate the effects of spider venom components on victims of Alzheimer's disease and amyotrophic lateral sclerosis, commonly referred to as Lou Gehrig's disease.


Akre, R.D. and E.A. Myhre. (1993) Biology and Medical Importance of the Aggressive House Spider, Tegenaria agrestis, in the Pacific Northwest (Arachnida: Araneae: Agelenidae), Washington State University, Pullman, Washington.

Russell, F.E. (1991) Venemous Arthropods, Vet. Hum. Toxical 33(5).

Vest, D.K. (1987) Envenomation by Tegenaria agrestis (Walckenaer) Spiders in Rabbits. Toxicon, Vol. 25, No. 2.pp.221-224, Great Britain.

Wegner, G.S. (1991) Ouch! (Spotlight on Spiders), Pest Control Technology 19(8):39.

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