Along Came a Spider...


Along Came a Spider...

By Rod Brouhard Feb 28, 2010

      In 2006, there were more than 82,000 calls to U.S. poison control centers reporting spider bites.1 Maybe you ran a few of those calls. What species is the most common in your neighborhood? Have you seen the dreaded Springfield recluse? How about the Philadelphia or Sacramento recluses?

   These are all closely related to the Los Angeles, Chicago and New York recluses. Related, of course, because they don't exist. Ever since purveyors of urban myth discovered e-mail and YouTube, recluse spiders (also known as brown recluses, brown spiders or Loxosceles spiders) are blamed for almost all lesions of unknown origin.2 We even get calls to 9-1-1 for "spider bites" from patients who are, in reality, suffering from some sort of inflammation that has nothing to do with spiders.

   Spider bites dwell more in the realm of the emergency department than the back of an ambulance, but acute envenomation does happen and can be quite painful. There is a possibility of death in some poisonous spider bites, but as a group they are much more likely to be colossally annoying than fatal.


   Almost all spiders are poisonous.3 However, in most cases, the venom is either too weak, in too small a quantity or too specific to insects to be toxic to humans. Even in species that have toxic venom, their fangs and other mouth parts may not be big or strong enough to bite humans.4

   In spiders, size doesn't matter—some of the biggest are the least dangerous. Those hairy tarantula-size monsters that crawled around on Indiana Jones are teddy bears compared to a black widow.4

   There are known to be only two medically significant species of spider in the United States. Most widespread is the black widow, common throughout the entire country. Cousins of the black widow live in all parts of the world. The infamous brown recluse, known best for necrotic arachnidism—a fancy term for ulcerated lesions caused by spider bites—is found only in the southeastern region of the U.S.2 There are a few other Loxosceles spiders found in the south, but none with the reputation of the brown recluse.

   All Loxosceles spiders have essentially the same toxic venom. For our purposes, they should be considered the same. Definitively identifying a brown recluse is too difficult for the average healthcare provider and should be left to the professional arachnologist.

   Despite its well-documented and very limited habitat, the brown recluse is blamed for lesions presenting in emergency departments from California to Maine. The Internet is full of brown recluse bite "victims" vigorously defending their homegrown diagnoses without suitable specimens to identify. The desire to know what causes such lesions is so strong, it concocts recluse spiders where none exist.

   In recent years, that need for answers and the well-known lack of brown recluse habitat in most of the country brought a new spider villain to the forefront: The hobo spider (Tegenaria agrestis) is notoriously hard to identify—harder even than the brown recluse—and is gaining ground as a supposed producer of necrotic arachnidism.5

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   Physicians are not immune to the hype. There have been misdiagnoses of lesions as spider bites, even when the spider in question didn't live in the area. For instance, while several brown recluse bites have been diagnosed in the San Francisco Bay area, no recluse or hobo spiders have been found there.6


   Black widow spiders (of the genus Latrodectus) are different than recluse spiders because their venom affects the body systemically rather than locally.4 There is a real danger of systemic reaction and death from black widow bites. However, though death is possible, it's unlikely.

   The exact mechanism of black widow venom is not completely understood. There is an oversimplified view in the prehospital setting that black widow venom is essentially a calcium channel blocker similar to Cardizem. The common belief is that calcium gluconate or calcium chloride is the best treatment. In reality, calcium gluconate doesn't work as well as opioids and benzodiazepines to relieve the pain of a black widow bite. The only drug that's shown to reduce the duration of a reaction is the antivenin. First aid measures, such as ice or elevation, have not been shown to have any effect.3

   Black widow spider envenomation, or latrodectism, causes presynaptic discharge of neurons and muscle cells, resulting in severe cramping and pain. Most cramping from black widow bites occurs in the abdomen, back and legs.3 Spider bites of all types mostly go unnoticed until the victim exhibits signs of toxicity. In latrodectism, the toxic reaction is systemic, with mild local irritation or sweating. In loxoscelism (brown recluse envenomation), the reaction is usually local, with rare systemic signs and symptoms.4

   If not recognized and treated, black widow bites have the rare potential to be fatal.4, 7 Since bites in general are not common, it is important to consider black widow bites when patients present with sudden-onset abdominal or back pain (especially if associated with cramping) and hypertension (especially without a history of hypertension).

   Diaphoresis is fairly common in black widow bites, and patients may present with odd patterns. Black widow bite victims have been observed sweating only over the bite area or just on the extremity where the bite occurred.4 They will sometimes present diaphoretic only on the face or neck and dry everywhere else.5

   Additional but less common signs and symptoms of latrodectism are chest pain, nausea and vomiting, shortness of breath, and extremity pain or paresthesia. Compartment syndrome, priapism and weakness have also been reported from black widow bites, but all are rare reactions.8,9


   Prehospital treatment of black widow bites starts with identifying the fact that a spider was involved at all. In many cases, the prehospital assessment and history will provide the best clues for a diagnosis. We have the unique opportunity to talk to patients in their natural habitats, and the observations we make there often lead to much clearer histories.

   When ruling out causes of abdominal pain, take clues from the patient's home environment. A clean, uncluttered home is less likely to harbor spiders than the alternative.4 Ask the patient about activities that may have resulted in a spider bite. Working in dark, out-of-the-way places is likely to bring patients in contact with black widows or other arachnids.

   Use opioids for pain relief and benzodiazepines for muscle cramping.3 Monitor blood pressure closely for hypertension. For suspected black widow bites, local protocols may call for calcium gluconate or calcium chloride. More research on the use of calcium for latrodectism is necessary, but current evidence does not support the practice.3

   Correctly identifying black widow bites in the prehospital setting can lead to treatment with antivenin in the emergency department. Patients with severe envenomations who are treated with antivenin resolve much quicker than patients who don't get it, and are less likely to be admitted to the hospital.3

   Small welts with surrounding redness and irritation are often attributed to spider bites when, in reality, they may or may not be a bites and, if they are, may or may not be from spiders. There are plenty of other biting bugs out there, including several species of arachnid that are not spiders. Ticks, chiggers, mites and scorpions all belong to the arachnid class, and all bite.4

   Insect bites and stings are virtually indistinguishable from spider bites, unless a bee left its stinger and venom sac behind. Identification is impossible without a specimen, and even then, unless the culprit is caught in the act, the relationship between bug and bite is circumstantial.10

   Diagnosing spider bites inside or outside the hospital is notoriously difficult, and misdiagnosis has the potential for catastrophic consequences in the case of necrotic lesions.11 Missing a black widow bite is unlikely to result in death, but the patient may be uncomfortable far longer than necessary.

   As with all diagnoses, worst-case scenarios should be ruled out first. For example, both spider and tick bites can present with the classic "bull's-eye" pattern of surrounding inflammation. Spider bites presenting that way are often benign, while the same presentation from a tick bite may indicate Lyme disease, a potentially fatal illness.12


   In many cases, bites and stings are not the worst possible outcomes, unless anaphylaxis is suspected. Remember that surface infections from MRSA and other organisms often resemble bug bites. Local reactions suspected to be bites should still be treated as possibly infectious, just in case.

   Spiders just want to be left alone. They don't want to waste time and effort biting animals they could never eat. If the source of a patient's symptoms isn't a spider or another bug, it may be something contagious. Consider all the possibilities when spiders get blamed. And if one crawls on you, be sure to flick it off, rather than squishing it, to avoid getting your own spider bite.4


1. Bronstein AC, Spyker DA, et al. 2006 Annual report of the American Association of Poison Control Centers' National Poison Data System (NPDS). Clin Toxicol (Phila) 45(8): 815–917, Dec 2007.

2. Frithsen IL, Vetter RS, Stocks IC. Reports of envenomation by brown recluse spiders exceed verified specimens of Loxosceles spiders in South Carolina. J Am Board Fam Med 20(5): 483–8, Sep-Oct 2007.

3. Clark RF, Wethern-Kestner S, et al. Clinical presentation and treatment of black widow spider envenomation: A review of 163 cases. Ann Emerg Med 21(7): 782–7, July 1992.

4. Diaz JH. The epidemiology, syndromic diagnosis, management, and prevention of spider bites in the South. J La State Med Soc 157(1): 32–8, Jan-Feb 2005.

5. Vetter RS, Isbister GK. Do hobo spider bites cause dermonecrotic injuries? Ann Emerg Med 44: 605–607, 2004.

6. Vetter RS. Arachnids submitted as suspected brown recluse spiders (Araneae, Sicariidae): Loxosceles spiders are virtually restricted to their known distributions but are perceived to exist throughout the United States. J Med Entomol 42(4): 512–21, July 2005.

7. Ennik F. Deaths from bites and stings of venomous animals. West J Med 133(6): 463–8, Dec 1980.

8. Cohen J, Bush S. Case report: Compartment syndrome after a suspected black widow spider bite. Ann Emerg Med 45(4): 414–6, Apr 2005.

9. Hoover NG, Fortenberry JD. Use of antivenin to treat priapism after a black widow spider bite. Pediatrics 114(1): e128–9, July 2004.

10. Stawiski MA. Insect bites and stings. Emerg Med Clin North Am 3(4): 785–808, Nov 1985.

11. Vetter RS, Bush SP. Reports of presumptive brown recluse spider bites reinforce improbable diagnosis in regions of North America where the spider is not endemic. Clin Infec Dis 35: 442–445, 2002.

12. Osterhoudt KC, Zaoutis T, Zorc JJ. Lyme disease masquerading as brown recluse spider bite. Ann Emerg Med 39: 558–561, May 2002.

13. Moran GJ, et al. Methicillin-resistant S. aureus infections among patients in the emergency department. NEJM 355: 666–74, 2006.

14. Baxtrom C, Mongkolpradit T, et al. Common house spiders are not likely vectors of community-acquired methicillin-resistant Staphylococcus aureus infections. J Med Entomol 43(5): 962–5, Sep 2006.

15. Pagac BB, Reiland RW, et al. Skin lesions in barracks: Consider community-acquired methicillin-resistant Staphylococcus aureus infection instead of spider bites. Mil Med 171(9): 830–2, Sep 2006.

16. Boyce JM, et al. Environmental contamination due to methicillin-resistant Staphylococcus aureus: Possible infection control implications. Infect Control Hosp Epidemiol 18(9): 622–7, Sep 1997.

17. Roline CE, Crumpecker C, Dunn TM. Can methicillin-resistant Staphylococcus aureus be found in an ambulance fleet? Prehosp Emerg Care 11(2): 241–4, Apr-Jun 2007.

   Rod Brouhard is a paramedic and EMS educator in Modesto, CA. He covers first aid and emergency response issues for

Signs and Symptoms of Spider Envenomation
Black Widow Bite (latrodectism) Brown Recluse Bite (loxoscelism)
Abdominal or back pain Painful bite
Muscle cramping Local irritation
Weakness Joint pain
Diaphoresis Chills and fever
Hypertension Rash
Local irritation, swelling or sweating Nausea and vomiting
Altered mental status

The Threat of MRSA

   A patient may insist his growing skin ulcer is from a spider bite, confirmed by his physician, but other causes must be considered for lesions that do not respond to treatment. The most common cause of spider-bite-looking skin lesions is methicillin-resistant Staphylococcus aureus (MRSA).

   MRSA has emerged as the leading cause of skin infections seen in the emergency department. In many cases, victims explain their lesions as spider bites. Doctors are almost as bad in perpetuating the myth. Even when MRSA is identified, spider bites are often blamed for introducing the infection.13

   Indeed, spiders aren't even necessarily accessories to the crime. There's no evidence to suggest spiders carry or spread MRSA.14 An outbreak of skin lesions in one military barracks prompted an intense pest control program, which failed to affect the outbreak.15 MRSA was later identified as the culprit.

   As a group, EMS providers tend to ignore most skin lesions unless the patient complains specifically about them. We are there for the cough, the chest pain or the shortness of breath. If a lesion is noticed, asking the patient about it will likely result in the patient saying it's "just a spider bite." That is likely not the case.

   It is prudent for EMS providers inside and outside the hospital to use precautions for skin lesions consistent with MRSA.16 Ambulances are ripe with MRSA contamination.17 Taking precautions not only protects providers and successive patients from possible contamination, it protects patients whose nonintact skin is not already infected.

   Cleanliness is the biggest precaution for preventing the spread of MRSA.10 Gloves and hand-washing are the absolute minimum precautions that should be taken for patients. Using gloves has always been the standard, but only required on patients when contact with bodily fluids is likely. With the amount of MRSA contamination found in ambulances, wearing gloves for any patient contact is not unreasonable.11

   Just wearing gloves is not enough, however. Cleaning the ambulance between patients is nearly as important. Touching surfaces with gloved hands can lead to contamination of the gloves with MRSA. Transferring that contamination to the next patient in the back of that ambulance would be easy if surfaces aren't cleaned between patients.

   Isolating patients presenting with "spider bites" will help decrease cross-contamination. Use of sheets and blankets to cover patients is more than a comfort measure. In the hospital, gowns and scrubs regularly become contaminated through common nursing procedures.10 There's no reason to think an EMS jumpsuit is any less contaminated unless precautions are taken to prevent contact with patients and environments where colonization of MRSA is suspected.

   If you wear a MRSA-contaminated uniform home, you contaminate your living space. Laundering uniforms outside the home is probably the best way to prevent bringing your work home with you.

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