Are You Confident of the Diagnosis?

Spider bites can cause myriad symptoms, ranging from a mild discomfort or burning to life-threatening systemic organ failure, hemolytic anemia, and death. Most species of spiders are not known to bite humans, and only a small portion of those species that do bite humans are known to cause serious disease.

Spiders are eight-legged predatory arthropods of the order Araneae. Spiders are equipped with paired fangs designed for capturing and envenoming their prey (Figure 1).

Figure 1.

Impressive fangs of a funnel-web spider (Atrax robustus). These aggressive spiders from southeast Australia can cause severe bite reactions. (Courtesy of Col Halliday. Reprinted from, with permission.)

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Fortunately for humans, most spider bites are relatively mild. Symptoms are often likened to a wasp or bee sting: there is immediate pain, often followed by redness, swelling, and discomfort which can last for a few hours and then subside. Occasionally, systemic symptoms such as fever, headache, malaise, nause and vomiting are reported.

Only a few groups of spiders cause medically important bite reactions. The most serious spider bites in the United States are caused by the black widow (Latrodectus mactans) (Figure 2). Black widow spiders are found throughout the United States but are more common in the southern and western states. However, the black widow is only one of several species within the genus Latrodectus (referred to as widow spiders) that are known to cause serious bite reactions in humans. Other species are listed in Table I.

Figure 2.

Characteristic hourglass shape on the underside of a black widow spider (Latrodectus mactans). The black widow is easily recognized by its thin black legs and round, pea-shaped abdomen. Other widow spiders, such as the Australian redback (L. hasselti), have similar red markings on the underside of the abdomen. (Courtesy of the CDC/James Gathany.)

Table I.
Common Name Species Distribution
Western widow L hesperus western U.S.
Redback spider L hasselti Australia
Katipo spider L katipo New Zealand
Mediterranean black widow L tredecimguttatus southern Europe, Africa, east and southeast Asia
Button spider L cinctus, L. indistinctus, others southern Africa

Most spiders in the genus Latrodectus have a similar appearance: a small, round, black body, thin black legs, and a characteristic red patch on the abdomen. In the black widow, the shape is likened to an hourglass, while in other species, the shape can be polka-dots or just a large streak of color.

The initial bite of the black widow may produce an immediate, sharp pain or may be painless. At first, the bite reaction is minimal, with slight erythema and swelling and the appearance of a set of small, red fang marks. However, within 2 hours of envenomation, systemic manifestations begin to appear as vascular dissemination of the venom occurs.

Symptoms begin with dull muscle cramping or severe pain with numbness (usually around the area of the bite but may extend to involve larger muscle groups). Severe abdominal pain with abdominal muscle spasm can occur, which may mimic a surgical abdomen. Other signs and symptoms include nausea and vomiting, dizziness, headache, diaphoresis, hypertension, tachycardia, tremors, muscle fasciculations, ptosis, and agitation/irritability. These symptoms become progressively more severe up to 24 hours after the bite, and then gradually decrease in severity over 2 to 3 days.

Residual symptoms including paresthesias, pain, weakness, and transient muscle spasms may persist for weeks to months after the bite. Rarely, more serious complications such as convulsions, paralysis, hypertensive emergency, respiratory failure, or shock occur. Death is extremely uncommon. Children and the elderly are at increased risk for severe complications from black widow spider envenomation.

Most other widow spider bites are typically more mild, sometimes causing radiating pain and less commonly high blood pressure, agitation, paresthesia, paralysis, or cardiac problems. For instance, the Australian redback spider (L hasselti) causes symptoms that almost always resolve within a week and fatalities are extremely rare.

Recluse spiders (genus Loxosceles) are another dangerous group of spiders capable of severe bite reactions. Members of the genus Loxosceles are widespread: there are 13 species of Loxosceles in North America, the most infamous of which is the brown recluse spider (L. reclusa). The brown recluse spider is found throughout the United States, but resides predominately in the south-central states. There are 38 species in Central America and 34 in South America including L laeta (the most toxic, found throughout most of South America), L intermedia (in Brazil and Argentina), and L gaucho (in Brazil). There are 12 species of Loxosceles in Africa and two species in China. Loxosceles rufescens is found throughout the Mediterranean region and also sporadically around the world.

Recluse spiders are an average of 9 mm in length and either tan, gray or brown in color with a characteristic violin or fiddle-shaped pattern on the dorsal cephalothorax (see Images (Figure 3, Figure 4). Some species of recluse spiders, however, have very light pigmentation in the violin area and others have dark maculae on the dorsal surface which may obscure identification. In addition, in contrast to most other spider species, recluse spiders have six eyes arranged in pairs in a U-shaped pattern, rather than the eight eyes seen in other spiders.

Figure 3.

Brown recluse (Loxosceles reclusa) spiders have a characteristic violin-shaped brown area on the dorsal thorax and have only three pairs of eyes. (Courtesy of Lisa Ames.)

Figure 4.

Another brown recluse spider. (Courtesy of Dirk Elston.)

Recluse spiders are shy and typically bite only when cornered. Initially, bites are usually painless. The severity of the bite reaction is variable, depending on the amount of venom injected, host susceptibility (children and the elderly often have more severe reactions) and the site of the bite. In mild cases, the bite causes only a mild urticarial reaction. In more severe cases the painless bite is followed 2 to 8 hours later by a sharp pain or burning sensation. Localized vasoconstriction causes the bite site to pale while the area immediately surrounding the bite becomes erythematous.

Commonly within 24 to 72 hours a central hemmorhagic vesicle or bulla develops and the center of the bite site becomes depressed, firm, and turns a blue violet color signaling the beginning of necrosis. This combination of erythema, ischemia and necrosis is called the “red, white and blue” sign (Figure 5). During the next 2 to 3 days the lesion may evolve into an eschar which will eventually slough off leaving an ulcer. Ulcers are usually 1 to 2 cm wide; however, some ulcers enlarge up to 30 cm in diameter. Wounds are slow to heal, over days to weeks.

Figure 5.

Brown recluse spider bites can cause central hemorrhagic necrosis with a painful ulcer surrounded by erythema. (Courtesy of Dirk Elston.)

Systemic symptoms due to recluse spider bites can be seen in the first 48 hours after envenomation. These symptoms include a diffuse macular eruption, nausea and vomiting, fever, headaches, malaise, hemolysis, thrombocytopenia, coagulopathy, and leukocytosis. Renal insufficiency, seizures, and death are rare.

The Australian funnel-web spider is one of the most venomous spiders in the world. Funnel-web spiders are actually several species within two closely related genera, Atrax and Hadronyche. These spiders are uniformly dark or black, stocky, and fairly large, with a body size between 0.5 and 3 inches in length (Figure 6).

Figure 6.

The Australian funnel web spider is a large, stocky, dark brown to black spider found in Australia. This is a female Atrax robustus. (Courtesy of Col Halliday. Reprinted from, with permission.)

The most severe funnel-web spider bites are caused by species found in New South Wales and southern Queensland. Male funnel-web spiders bite much more commonly than females. Bites are considered a medical emergency, as symptoms arise in a mean of 28 minutes. Patients typically present during the warmer months with a bite on the distal extremity after engaging in outdoor activity. Large fangs and a powerful bite cause puncture marks and severe pain which usually resolves in a few hours. Systemic symptoms arise in an estimated 10 to 25% of victims.

Symptoms, in order of prevalence, include diaphoresis, high blood pressure, tachycardia, pulmonary edema, and muscle fasciculations. Agitation, hypersalivation, vomiting, pupillary changes, hypotension, and unconsciousness can also occur. Death may rapidly ensue from hypotension or cerebral edema unless antivenin is promptly given. The mouse spider (Missulena bradleyi) is another large, black, bulky spider found in Australia. Fortunately, this spider is less aggressive than the funnel web, and systemic symptoms from envenomation are rare.

In Brazil, the wandering spider (Phoneutria sp, aka the banana spider or armed spider) is responsible for thousands of bites each year. These large, aggressive spiders do not spin webs and can crawl and jump very quickly. When cornered, these spiders assume a characteristic warning posture, rearing up with the front 4 legs held almost straight up in the air. Bites cause immediate severe pain at the bite site. Systemic symptoms are seen in only 1 to 3% of victims, mostly children, and include hypertension, tachycardia, agitation, priapism, diaphoreses, hyperhidrosis, pulmonary edema, and shock. Death is extremely uncommon.

The hobo spider (Tegenaria agrestis) is native to Europe but was introduced and subsequently settled in the Pacific Northwest US, from Oregon east to Montana and Colorado, north to British Columbia, Canada. medium-sized spiders have a variable appearance and are best identified by an expert. Bites from the hobo spider have been implicated in cases of dermal necrosis, although there is considerable controversy as to the validity of these reports. Hobo spider bites in Europe, where the spider is common, are virtually unknown.

Tarantulas (family Theraphosidae) are the largest of spiders. These spiders, typically very hairy, are found throughout tropical and subtropical deserts and forests. Tarantulas can grow to several inches in size, the largest with legs spanning nearly a foot (Figure 7).

Figure 7.

A male Arizona blonde tarantula (Aphonopelma chalcodes) crossing the road. Many species of tarantulas can cause painful bites, likened to a bee sting, but they are not a true threat to humans. The abdominal hairs, however, can get into mucous membranes and cause severe irritation. (Courtesy of Nichole L. Hossler.)

Although fearsome in appearance, most tarantulas are docile and will not bite humans unless provoked. Fortunately, tarantula venom is very mild and the bites are likened to a bee or wasp sting. Symptoms generally resolve in a few hours with symptomatic therapy. More worrisome is cutaneous or mucous membrane irritation from abdominal setae, which the tarantula, when threatened, releases into the air by rubbing its legs vigorously against the abdomen. These hairs are barbed and thought to cause mechanical irritation.

Reactions can be particularly serious in the eye, a condition called ophthalmia nodosa. The hairs embed in the cornea and may cause foreign body sensation, chemosis, corneal abrasions, iritis, and decreased visual acuity. Rarely, granulomas, vitritis, or endophthalmitis can result.

Yellow sac spiders (genus Cheiracanthium) are found in Europe,Australia, the US, and elsewhere. They are typically 5 to 10 mm in size,and have a pale yellow or tan color. These spiders are aggressive andprobably are one of the most common species to bite humans, sometimeswithout provocation. The reaction is typically likened to a wasp or beesting and will last only a few hours. Despite some reports, there islittle evidence to suggest that yellow sac spiders can causeulceronecrotic lesions.

Diagnosis confirmation

Diagnosis of spider bites relies heavily on the history of an actual bite being observed. Ideally, any spider that does bite should be captured (alive or dead) to allow for proper identification by a reliable expert. Misdiagnosis, mistreatment, and missed diagnosis can result unless the spider is “caught in the act.” With the advent of the internet, photographs of most offending spiders can easily be found for comparison to a collected specimen. If a spider was not observed inflicting the bite, or a spider was not recovered and properly identified then other conditions which may mimic spider bite must be excluded.

Spider bite reactions may be simulated by a multitude of other cutaneous and systemic diseases and there are no specific tests that reliably diagnose spider bites. Of note, an ELISA wound swab for brown recluse venom has shown some promise, but this test is not yet commercially available.

The effects of black widow envenomation can mimic a number of other disease states. The abdominal pain and abdominal muscle rigidity may be mistaken for an acute abdomen (eg, appendicitis, peritonitis, etc.). The muscle spasms caused by black widow venom may cause severe chest pain, which when coupled with hypertension, diaphoresis, and nausea may resemble an acute myocardial infarction. In addition the increased muscle tone and spasms, tachycardia, and diaphoresis seen following a black widow bite may be mistaken for tetanus.

The most characteristic lesion of a recluse spider bite, the dermonecrotic lesion, may be simulated by a multitude of other cutaneous and systemic diseases. Studies have shown that most clinically diagnosed recluse bites are erroneous (see Unusual Scenarios).

The differential diagnosis of ulceronecrotic lesions due to brown recluse spider bites includes staphylococcal (especially methicillin-resistant Staphylococcus aureus) or streptococcal infection, herpes simplex, ecthyma gangrenosum, anthrax, invasive fungal infection, diabetic ulcer, chemical burn, neoplasia, erythema nodosum, pyoderma gangrenosum, and vasculitis. Cultures for infectious organisms as well as a thorough medical history will differentiate most of these entities. A biopsy may be helpful to rule out deep infection, vasculitis, panniculitis, and neoplasia. Because spiders rarely bite more than once, a history of multiple lesions concurrently or lesions in patients living communally should lead one to think of a contagious disease rather than spider envenomation.

Who is at Risk for Developing this Disease?

Every year, thousands of spider bites are reported to the American Association of Poison Control Centers, and likely many more go unreported. However, many reported bites are erroneous; a recent study found that of 182 patients reporting to a US emergency department, only 7 (3.8%) had confirmed spider bites. The overwhelming majority of these spider bites proved to be skin and soft tissue infections. Nevertheless, spiders and humans frequently interact, and spider bites are common in many suburban and rural environments worldwide.

Widow spiders are shy, sedentary, and nocturnal, rarely leaving theirwebs. They prefer dry and dark places such as woodpiles, under stones,in debris, in barns and garages, and in abandoned or infrequently usedbuildings. Bites commonly occur when spiders are compressed against theskin or injured such as when people put on bike helmets, gardeninggloves, shoes, or stored clothing. Bites tend to occur during the warmermonths. Most black widow bites occur on the extremities, although inthe past most bites occurred on the buttocks and genitalia while victimswere using outdoor toilets.

Recluse spiders are found in dry, dirty, undisturbed environments such as abandoned or infrequently used buildings, basements, attics, rock or wood piles, and stored clothing. Brown recluse spiders tend to be shy, nonaggressive and avoid humans; however, they will attack when they feel threatened or are injured. Bites frequently occur while a person is cleaning out a storage area or when a person puts on clothing that has been stored undisturbed for a long period of time. Most brown recluse bites occur between April and October, as these spiders hibernate in the fall and winter.

Phoneutria bites occur mostly on the hands and feet. Children and the elderly are more likely to have systemic reactions to envenomation. These spiders may hide in banana bunches. Although these spiders are mostly nocturnal, most bites occur in and around the home during the day. Bites are most common during the spider’s breeding season, in March and April.

Tarantulas are increasingly common as pets, and most reported exposures occur in pet owners.

What is the Cause of the Disease?

Spider venoms contain a number of active proteins and chemicals responsible for clinical symptoms. Only a few venoms have been intensively studied.

Widow spiders produce a toxin called alpha-latrotoxin, which has been isolated from the Mediterranean black widow (L tredecimguttatus) and is probably present in the venom of all widow spiders. The toxin binds to its receptor on the presynaptic motor neuron cell membrane, causing calcium-independent exocytosis of dense core granules, releasing neuropeptides into the presynaptic space. The toxin itself also acts as a calcium channel, and calcium influx also contributes to exocytosis. Increased synaptic concentrations of acethylcholine, norepinephrine, dopamine, and glutamate result, causing muscle cramps and spasm, with nausea, vomiting, hypertension, weakness, malaise, and tremors, usually lasting from days to a week.

The venom of the brown recluse contains several enzymes and proteins, the most important of which is the enzyme sphingomyelinase D (SMD). SMD interacts with sphingomyelin on cell membranes causing endothelial cell disruption, intravascular hemolysis, platelet aggregation and thrombi formation. It is believed that SMD also disrupts neural transmission and degrades myelin sheaths. Brown recluse spider venom also contains hyaluronidase which may increase the permeability of the subcutaneous tissues allowing the venom to spread. In addition, the venom activates complement and attracts neutrophils to the site of envenomation, both of which contribute to tissue necrosis.

Funnel-web spiders produce a number of peptide toxins termed atracotoxins. These toxins affect voltage-gated sodium channels, resulting in excessive and repetitive action potentials, excessive release of neurotransmitters, and ultimately in the autonomic and somatic symptoms seen clinically.

The venom of wandering spiders contains tachykinin, excitatory amino acids, spinal neurokinins, and nitric oxide. Venom also increases activity of neuronal sodium channel, causing muscle contraction, activation of the autonomic nervous system, and release of catecholamines.

Systemic Implications and Complications

Systemic signs and symptoms of black widow spider envenomation include arthralgias, muscle rigidity, bronchorrhea, diaphoresis, fever, hypertension, tachycardia, hyperreflexia, nausea, vomiting, paresthesias, ptosis, restlessness, tremors, and salivation. Death is rare. Abnormal laboratory findings that may be present following a black widow spider bite include elevated white blood cell count, creatinine kinase, serum glucose, and liver enzymes.

While brown recluse spider bites generally cause only a cutaneous injury, occasionally envenomation results in a severe systemic reaction. Systemic symptoms of a brown recluse spider bite include fever and chills, weakness, malaise, nausea and vomiting, arthralgias, myalgias. In addition brown recluse spider venom can cause hemolytic anemia, thrombocytopenia, disseminated intravascular coagulation, and, rarely, death. A few cases have resulted in limb amputation.

Funnel web spider bites are considered a medical emergency as systemic symptoms can rapidly occur within minutes of envenomation. Systemic effects can be divided into the following categories: (1) autonomic effects, including diaphoresis, hypersalivation, lacrimation, piloerection, miosis, and mydriasis; (2) cardiovascular effects including hypertension, hypotension, tachycardia or bradycardia; (3) neuromuscular symptoms such as muscle fasciculations and paresthesias. Pulmonary and cerebral edema, unconsciousness, and death may also occur rarely.

Wandering spider bites only rarely cause systemic symptoms such as hypertension, tachycardia, agitation, priapism, diaphoresis, hyperhidrosis, pulmonary edema, and shock.

Ophthalmia nodosa from tarantula hairs can result in severe visual disturbances, including reduced visual acuity and rarely blindness. Symptoms may last for months.

Treatment Options

Treatment options are summarized in Table II.

Table II.
Capture and identification of the biting spider
Antivenin (if appropriate – see Therapeutic Approach below)
Ice and local analgesics
Oral analgesia
Wound care, gentle debridement (for dermonecrotic wounds)

Optimal Therapeutic Approach for this Disease

Most spider bites are relatively mild. If possible, the spider should be collected (dead or alive) and identified by a reliable expert. Initial management of any spider bite should be symptomatic. The bite site should be washed gently with soap and water, and ice can be applied for 15-minute intervals with a cloth between the ice and the skin. Topical anesthetics such as lidocaine 4% gel or pramoxine 1% lotion in combination with oral analgesics (such as acetaminophen or ibuprofen) can be helpful to reduce pain. Severe pain may require short-term narcotic analgesia. Tetanus prophylaxis should be considered. Unless the spider bite was caused by a widow, recluse, funnel web, or wandering spider, most spider bites will resolve in a matter of hours and no further care is warranted.

Initial treatment following the bite from a widow spider should begin with the regimen listed above. Muscle spasms may cause severe pain and muscle relaxants (eg, methocarbamol) and benzodiazepines (eg, lorazepam) can be used to reduce pain in severe envenomations. Widow antivenin is commercially available for use throughout the world; however, its use is usually reserved for severe envenomations leading to life-threatening symptoms or envenomations that cause intractable pain. Widow antivenin should be given as soon as possible following the onset of symptoms that indicate a need for antivenin administration; however, it will be effective even if given 90 hours after a bite.

Symptoms usually begin to subside within 3 hours of treatment with antivenin. The initial dose consists of 6000 antivenin units or one vial (2.5 ml) given intramuscularly or intravenously in 100 to 250ml of saline over 60 minutes. Usually one dose is sufficient; however, occasionally a second or third dose is necessary. Widow antivenin should be used cautiously due to the risks associated with its administration, including anaphylaxis and serum sickness. Some authors recommend a short course of prednisone (40 to 60mg orally daily) for up to a week to prevent serum sickness in patients who have received antivenin.

The treatment of recluse spider bites is somewhat controversial. Although an antivenin is available in Brazil for bites of L gaucho, the effectiveness of the antivenin has been called into question. Meticulous wound care with judicious debridement of necrotic tissue is useful; however early surgical excision has not shown to be effective. Occasionally, skin grafting is needed for nonhealing wounds.

Anecdotal evidence has reported that dapsone may decrease tissue necrosis by inhibiting neutrophil chemotaxis and neutrophil myeloperoxidase, thus inhibiting the formation of oxygen intermediates. However, in an animal model, dapsone was ineffective at preventing ulcer formation or accelerating healing. Furthermore, dapsone has a risk of severe side effects, including hemolysis, methemoglobinemia, neuropathy, and agranulocytosis; patients with glucose-6-phosphate dehydrogenase deficiency are especially at risk of hemolytic anemia from dapsone.

Many other therapies have been suggested for recluse bites but have not been shown to be consistently effective in human or animal studies. These include systemic or intralesional steroids, antihistamines, nitroglycerin, hyperbaric oxygen, and electric shock treatment. An antivenin has been developed, but is not commercially available. A recent study using an animal model suggested that topical tetracycline may be effective for treating recluse spider envenomations. However, despite the numerous therapies reported in the literature, there is no effective evidence-based therapy at this time.

Funnel web spider bites are considered a medical emergency. If possible, pressure immobilization technique to retard lymphatic flow from the bitten limb should be initiated to prevent proximal spread of the venom while the patient is transferred to a medical facility that has antivenin. The patient should be closely monitored for systemic symptoms: if no systemic symptoms occur after 4 hours of observation, the patient may be discharged.

If systemic symptoms occur, two vials of antivenin should be administered. Additional vials should be prepared in case the victim does not improve or if symptoms worsen. Approximately 1% of persons given antivenin have an allergic reaction to the antivenin, which may cause hypotension, throat tightness, or serum sickness. Antivenin is 97% effective in complete reversal of symptoms due to funnel web spider bites, regardless of the species of spider responsible.

Most bites from wandering spiders can be managed with the above listed pain control measures. Antivenin is available, and it should be given in cases with severe symptoms such as hypertension, convulsions, shock, pulmonary edema, or priapism. Hypersensitivity reactions to antivenin are possible, and these patients should be treated in a facility capable of managing allergic reactions.

To avoid tarantula hairs, these spiders should be handled with the greatest of care. Goggles and gloves can be helpful when cleaning tarantula aquariums or when handling them. If exposure occurs, care should be taken not to try to rub off the hairs; rubbing may drive the tiny barbed hairs deeper into the skin. Instead, use the sticky side of tape (tape stripping) to remove the hairs. If the eyes or other mucous membranes are affected, immediate consultation with ophthalmology or the appropriate specialist is warranted. The hairs should be removed, if possible. Ophthalmia nodosa generally responds to topical steroids.

Patient Management

Because most spider bites are mild, no follow-up is needed in the majority of cases. Wound infection after spider bites is extremely uncommon, and routine use of prophylactic antiobiotics is discouraged. Spiders are not known to carry any communicable diseases.

Extremes of age have been associated with more severe reactions after black widow and brown recluse spider bites. If systemic symptoms are present in these patients, or if the patient has underlying cardiovascular disease, overnight observation should be considered. Victims of funnel web spider bites should be monitored for at least 4 hours after the bite; after this time frame, the development of systemic symptoms is very uncommon.

Patients with confirmed recluse spider bites should be counseled about the potential for developing a chronic wound with its attendant sequelae, including a slow healing process over weeks or months and the potential for severe scarring in 10 to 15% of victims.

It has been suggested that patients treated with antivenin should concurrently be treated with a tapering dose of prednisone to prevent serum sickness from the antivenin. These patients should be encouraged to contact their provider if they experience fever, malaise, arthragias, or rash during the first few days or weeks after antivenin administration.

Unusual Clinical Scenarios to Consider in Patient Management

Many patients who present with an ulceronecrotic skin lesion of unknown source will erroneously blame a spider bite. The reason why patients falsely blame spiders is unknown – in many cases, a spider is never seen, nor a bite felt. Many of these so-called “spider bites” (Figure 8) turn out to be furunculosis caused by methicillin-resistant Staphylococcus aureus (MRSA), pyoderma gangrenosum, or other condition (see differential diagnosis above).

Figure 8.

An expanding ulcer of pyoderma gangrenosum, referred to our department as a “black widow spider bite.” The ulcer completely healed with prednisone. Investigation revealed underlying myelodysplastic syndrome.

A recent study found that almost 90% of patients presenting to the emergency room with a lesion attributed to a spider bite turned out to have a soft tissue infection. Only 3.8% of patients actually had confirmed spider bites. Another study found that almost half of patients who had methellin-resistant S aureus (MRSA0) skin infections initially presented with a chief complaint of “spider bite.”

Another recent paper documented a case of methemoglobinemia stemming from dapsone treatment of a suspected brown recluse bite that turned out to be MRSA infection. The patient was glucose-6-phosphate dehydrogenase deficient. Care should be taken to correctly diagnose ulceronecrotic lesions if there is no reliable history of spider bite. A diagnosis of brown recluse spider bite should be made with certainty only if the offending spider is caught and identified by a reliable source.

There has been a large body of recent literature acquitting certain spider species previously thought to cause dermonecrotic bite reactions. Historically, many dermonecrotic ulcerations have been ascribed to spiders bites, perhaps because of historical prejudice, perhaps because of ignorance. Circumstantial evidence, such as finding spiders in the home of the victim, were all that was needed to place blame sqarely on the innocent arthropod.

For years, Australian physicians blamed dermonecrotic lesions on the bite of the white-tailed spider (genus Lampona) and only recently was a study performed of bites in which the offending spider was caught and identified. In that series of confirmed bites, there were no necrotic lesions. Similar evidence is mounting against the hobo spider causing dermonecrotic lesions. Furthermore, many reported brown recluse dermonecrotic lesions are reported from areas where this spider is virtually unknown. Many of these cases may have been MRSA furunculosis or other potentially serious illness that have gone undiagnosed and untreated. This underscores the importance of capturing and identifying the spider, if indeed one is to blame.

What is the Evidence?

Braitberg, G, Segal, L. “Spider bites – Assessment and management”. Aust Fam Physician. vol. 38. 2009. pp. 862-7. (Concise review of Australia’s two most important spiders – the redback and the funnel web. Addressess diagnosis and management issues.)

Vetter, RS, Isbister, GK. “Do hobo spider bites cause dermonecrotic injuries?”. Ann Emerg Med.. vol. 44. 2004. pp. 605-7. (Critical review of the literature regarding hobo spider bites. Only circumstantial evidence supports the theory that these spiders, and other species, can cause dermonecrotic lesions. Physicians (and patients) may be inappropriately blaming these spiders, and more importantly missing alternate diagnoses.)

Vetter, RS, Isbister, GK. “Medical aspects of spider bites”. Annu Rev Entomol. vol. 53. 2008. pp. 409-29. (Recent thorough review on spider bites and their management. The bulk of the article focuses on the two most important biting spiders: widow and recluse spiders. There is also a good discussion regarding recent evidence exonerating the white-tailed spider, black house spider, yellow sac spider, wolf spider, and hobo spider, all of which had previously been blamed for severe dermonecrotic reactions. Consequences of missed and misdiagnosis are also discussed.)

Suchard, JR. ““Spider bite” lesions are usually diagnosed as skin and soft-tissue infections”. J Emerg Med. 2009. (In this recent prospective study, patients who presented to the emergency room with suspected or presumed spider bite were studied. Only 3.8% of these patients were confirmed to have spider bites; over 85% proved to have skin and soft tissue infections.)

Belyea, DA, Tuman, DC, Ward, TP, Babonis, TR. “The red eye revisited: ophthalmia nodosa due to tarantula hairs”. South Med J. vol. 91. 1998. pp. 565-7. (Well-written case report and review of ophthalmia nodosa from tarantula hairs. Tarantulas are increasing in popularity as pets and care should be taken while handling them. Mask and gloves may be helpful in preventing exposure to the irritating hairs.)

Isbister, GK, Graudins, A, White, J, Warrell, D. “Antivenom treatment in arachnidism”. J Toxicol Clin Toxicol. vol. 41. 2003. pp. 291-300. (Reviews the antivenins developed for spiders (and scorpions) that are used today. Venoms are available for widow spiders, funnel-web spiders, and wandering (banana) spiders. There is also a venom against a Brazilian recluse spider, L gaucho. Venoms for Latrodectus species appears to have effectiveness across several species. There is a low rate of hypersensitivity to antivenoms.)

Swanson, DL, Vetter, RS. “Loxoscelism”. Clin Dermatol. vol. 24. 2006. pp. 213-21. (Thorough review of the epidemiology, pathophysiology, diagnosis, and treatment of dermonecrosis caused by brown recluse spider bites.)

Blackman, JR. “Spider Bites”. J Am Board Fam Pract. vol. 8. 1995. pp. 288-94. (Review of the diagnosis and management of bites from medically important spider species in the United States including the brown recluse, black widow, hobo, and tarantula.)

Diaz, JH, Leblanc, KE. “Common Spider Bites”. Am Fam Physician. vol. 75. 2007. pp. 869-73. (Excellent review article covering widow spiders, recluse spiders and tarantulas. Gives a great comparison between the bites of widow and recluse spider bites.)