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A spider bite, also known as arachnidism, is an injury resulting from the bite of a spider. The effects of most bites are not serious.[1] Most bites result in mild symptoms around the area of the bite.[1] Rarely they may produce a necrotic skin wound or severe pain.[2]: 455
Most spiders do not cause bites that are of importance.[1] For a bite to be significant, substantial envenomation is required. Bites from the widow spiders involve a neurotoxic venom which produces a condition known as latrodectism.[3] Symptoms may include pain which may be at the bite or involve the chest and abdomen, sweating, muscle cramps and vomiting among others.[1] Bites from the recluse spiders cause the condition loxoscelism, in which local necrosis of the surrounding skin and widespread breakdown of red blood cells may occur.[4] Headaches, vomiting and a mild fever may also occur.[4] Other spiders that can cause significant bites include the Australian funnel-web spider[5] and South American wandering spider.[1]
Efforts to prevent bites include clearing clutter and the use of pesticides.[1] Most spider bites are managed with supportive care such as nonsteroidal anti-inflammatory drugs (including ibuprofen) for pain and antihistamines for itchiness.[6] Opioids may be used if the pain is severe.[6] While an antivenom exists for black widow spider venom, it is associated with anaphylaxis and therefore not commonly used in the United States.[6] Antivenom against funnel web spider venom improves outcomes.[1] Surgery may be required to repair the area of injured skin from some recluse bites.[6]
Spider bites may be overdiagnosed or misdiagnosed.[1] In many reports of spider bites it is unclear if a spider bite actually occurred.[7] Historically a number of conditions were attributed to spider bites. In the Middle Ages a condition claimed to arise from spider bites was tarantism, where people danced wildly.[8] While necrosis has been attributed to the bites of a number of spiders, good evidence only supports this for recluse spiders.[1]
Signs and symptoms
Almost all spiders are venomous, but not all spider bites result in the injection of venom. Pain from non-venomous bites, so-called “dry bites”, typically lasts for 5 to 60 minutes while pain from envenomating spider bites may last for longer than 24 hours.[9] Bleeding also may occur with a bite. Signs of a bacterial infection due to a spider bite occur infrequently (0.9%).[9]
A study of 750 definite spider bites in Australia indicated that 6% of spider bites cause significant effects, the vast majority of these being redback spider bites causing significant pain lasting more than 24 hours.[10] Activation of the sympathetic nervous system can lead to sweating, high blood pressure and gooseflesh.[11]
Most recluse spider bites are minor with little or no necrosis. However, a small number of bites produce necrotic skin lesions. First pain and tenderness at the site begin. The redness changes over two to three days to a bluish sinking patch of dead skin—the hallmark of necrosis. The wound heals slowly over months but usually completely.[12] Rarely, bites may cause widespread symptoms, with occasional fatalities.[13]
There are a few spiders that can bite human skin and cause a skin reaction, but spiders are blamed for many more reactions. In particular the misdiagnosis of infections and other skin ailments are commonly attributed to brown recluses.[14]
| Scientific name | Common name | Venom | Reaction |
|---|---|---|---|
| Lampona spp[15][16] | White-tailed | Welt | |
| Loxosceles spp[14] | Brown recluse | Sphingomyelinase | Necrosis |
| Cheiracanthium spp | Sac | Lipase | Redness |
| Tegenaria agrestis[17] | Hobo | Redness | |
| Lycosidae spp[18][19] | Wolf | Redness, itching |
Cause
Spiders do not feed on humans and typically bites occur as a defense mechanism.[20] This can occur from unintentional contact or trapping of the spider.[20] Most spiders have fangs too small to penetrate human skin.[21] Most bites by species large enough for their bites to be noticeable will have no serious medical consequences.[22]
Medically significant spider venoms include various combinations and concentrations of necrotic agents, neurotoxins, and pharmacologically active compounds such as serotonin. Worldwide only two spider venoms have impact on humans—those of the widow and recluse spiders. Unlike snake and scorpion envenomation,[23] widow and recluse species bites rarely have fatal consequences. In addition to the widespread widow and recluse spiders, some spider families found exclusively in remote tropical regions have a lethal neurotoxic venom: the wandering spider in Brazil and the funnel web in Australia. However, due to limited contact between these spiders and humans, deaths have always been rare, and since the introduction of anti-venom in Australia, there have been no funnel web related deaths.[24]
Pathophysiology
A primary concern of the bite of a spider is the effect of its venom. A spider envenomation occurs whenever a spider injects venom into the skin. Not all spider bites involve injection of venom, and the amount of venom injected can vary based on the type of spider and the circumstances of the encounter. The mechanical injury from a spider bite is not a serious concern for humans. However, it is generally the toxicity of spider venom that poses the most risk to human beings; several spiders are known to have venom that can cause injury to humans in the amounts that a spider could inject when biting. While venoms are by definition toxic substances, most spiders do not have venom that is directly toxic (in the quantities delivered) to require medical attention and, of those that do, severity is typically mild.
Spider venoms work on one of two fundamental principles; they are either neurotoxic (attacking the nervous system) or necrotic (attacking tissues surrounding the bite). In some cases, the venom affects vital organs and systems. The venoms of the widow spiders, Brazilian wandering spider and Australian funnel-web are neurotoxic. Heart muscle damage is an unusual complication of widow venom that may lead to death.[25] Pulmonary edema, which is fluid accumulation in the lungs, is a feared and potentially serious but uncommon complication of funnel-web venom.[24] Recluse and South African sand spider venoms are necrotic. Recluse venom may also cause severe hemolysis (destruction of red blood cells), though this is typically uncommon.[26]
Diagnosis
Reliable diagnoses of spider bites require three conditions: first, there should be clinical effects of the bite at the time or soon afterwards, although there are no symptoms universally diagnostic of a spider bite, and bites by some spiders, e.g. Loxosceles species, may initially be painless; second, the spider should be collected, either at the time of the bite or immediately afterwards; and third, the spider should be identified by an expert arachnologist.[27][7]
Spider bites are commonly misdiagnosed. A review published in 2016 showed that 78% of 134 published medical case studies of supposed spider bites did not meet the necessary criteria for a spider bite to be verified. In the case of the two genera with the highest reported number of bites, Loxosceles and Latrodectus, spider bites were not verified in over 90% of the reports. Even when verification had occurred, details of the treatment and its effects were often lacking.[7] Unverified bite reports likely represent many other conditions, both infectious and non-infectious, which can be confused with spider bites.[28] Many of these conditions are far more common and more likely to be the source of necrotic wounds.[4] An affected person may think that a wound is a spider bite when it is actually an infection with methicillin-resistant Staphylococcus aureus (MRSA).[29] False reports of spider bites in some cases have led to misdiagnosis and mistreatment, with potentially life-threatening consequences.[30]
Prevention
Efforts to prevent bites include clearing clutter and the use of pesticides.[1]
OSHA recommends that workers take following measures to prevent spider bite:
- Wear a long-sleeved shirt, hat, gloves, and boots when handling boxes, firewood, lumber, rocks, etc.
- Inspect and shake out clothing and shoes before getting dressed.
- Use insect repellents, such as DEET or Picaridin, on clothing and footwear.[31][32]
Management
Most spider bites are harmless, and require no specific treatment. Treatment of bites may depend on the type of spider; thus, capture of the spider—either alive, or in a well-preserved condition, is useful.[33][34]
Treatment of spider bites includes washing the wound with soap and water and ice to reduce inflammation.[35] Analgesics and antihistamines may be used; however, antibiotics are not recommended unless there is also a bacterial infection present.[35] Black widow post-envenomation treatment seeks to control resulting pain and nausea.
In the case of bites by widow spiders, Australian funnel-web spiders, or Brazilian wandering spiders, medical attention should be sought immediately as in some cases the bites of these spiders develop into a medical emergency.[36][37] Antivenom is available for severe widow and funnel-web envenomation.[1]
Necrosis
In almost all cases, recluse bites are self-limited and typically heal without any medical intervention.[4] Recommendations to limit the extent of damage include elevation and immobilization of the affected limb, application of ice. Both local wound care, and tetanus prophylaxis, are simple standards. There is no established treatment for more extensive necrosis. Many therapies have been used including hyperbaric oxygen, dapsone, antihistamines (e.g., cyproheptadine), antibiotics, dextran, glucocorticoids, vasodilators, heparin, nitroglycerin, electric shock, curettage, surgical excision, and antivenom. None of these treatments conclusively show benefit. Studies have shown surgical intervention is ineffective and may worsen outcome. Excision may delay wound healing, cause abscesses, and lead to objectionable scarring.[38]
Dapsone, an antibiotic, is commonly used in the United States and Brazil for the treatment of necrosis. There have been conflicting reports with some supporting its efficacy and others have suggested it should no longer be used routinely, if at all.
Antivenom
Use of antivenom for severe spider bites may be indicated, especially in the case of neurotoxic venoms.[40] Effective antivenoms exist for Latrodectus, Atrax, and Phoneutria venom. Antivenom in the United States is in intravenous form but is rarely used, as anaphylactic reaction to the antivenom has resulted in deaths. In Australia, antivenom in intramuscular form was once commonly used, but use has declined. In 2014 some doubt as to antivenom effectiveness has been raised.[41][42] In South America an antivenom is available for Loxosceles bites, and it appears antivenom may be the most promising therapy for recluse bites. However, in experimental trials recluse antivenom is more effective when given early, and patients often do not present for 24 or more hours after envenomation, possibly limiting the effect of such intervention.
Epidemiology
Estimating the number of spider bites that occur is difficult as the spider involvement may not be confirmed or identified.[21] Several researchers recommend only evaluating verified bites: those that have an eyewitness to the bite, the spider is brought in, and identified by expert. With “suspected arachnidism” the diagnosis came without a spider positively identified.[4]
Africa
Several Latrodectus species (button spiders) live in Africa. South Africa also has six-eyed sand spiders (Hexophthalma species), whose bite may potentially cause skin necrosis. Physicians are advised that the diagnosis may be difficult without a spider.
Australia
Bites by the redbacks (Latrodectus hasselti) number a few thousand yearly throughout the country. Antivenom use is frequent but declining. Children may have fewer complications from bites. Funnel web spider bites are few 30–40 per year and 10% requiring intervention. The Sydney funnel web and related species are only on the east coast of Australia.
Europe
In Switzerland about ten to one hundred spider bites occur per one million people per year.[47] During epidemics of latrodectism from the European black widow upwards of 150 bites a year were documented.[48]
North America
The American Association of Poison Control Centers reported that they received calls regarding nearly 10,000 spider bites in 1994.[21] The spiders of most concern in North America are brown recluse spiders, with nearly 1,500 bites in 2013[49] and black widow spiders with 1,800 bites.[49] The native habitat of brown recluse spiders is in the southern and central United States, as far north as Iowa. Encounters with brown recluse outside this native region are very rare and bites are thought to be suspect.[4] A dozen major complications were reported in 2013.
South America
Numerous spider bites are recorded in Brazil with 5000+ annually. Loxosceles species are responsible for the majority of reports. Accidents are concentrated in the southern state of Parana with rates as high as 1 per 1,000 people.[51] Bite from Phoneutria (Brazilian wandering spider) number in the thousands with most being mild. Severe effects are noted in 0.5% of cases, mostly in children.
History
Recorded treatment from the 1890s for spider bites in general was rubbing in tobacco juice to the bitten skin,[53] similar to some of the traditional uses of the tobacco plant for various bites and stings from Central and South America.[citation needed] Wild dancing and music was the cure for tarantism—the frenzy was believed to arise from the bite of a spider.[54] An antivenom was developed against wolf spiders in Brazil and used for decades. Wolf spiders have since been exonerated—they never caused illness.
Black Widow Spider vs. Brown Recluse Spider
In the U.S., most spiders you find are harmless, but the black widow spider and the brown recluse spider are exceptions. Both types of spiders are more common in the southern U.S. and in warm, dry climates. Within these areas they tend to be found in environments that are undisturbed such as basements, closets, attics, below sinks, or in wood piles.
Dangers of a Black Widow Bite
The bite of a black widow spider is dangerous because it can affect a person’s nervous system. The spider produces a neurotoxic protein that is extremely potent. Some people may have a minimal reaction, but others may suffer from a severe response.
Symptoms of a Black Widow Bite
Symptoms of a black widow spider bite start within an hour after being bitten. Symptoms include
- severe muscle cramps,
- abdominal pain,
- weakness, and
- tremor.
In severe cases symptoms may include
- nausea,
- vomiting,
- faintness,
- dizziness,
- chest pain, and
- respiratory difficulties.
Dangers of Brown Recluse Spiders
Another toxic spider is the brown recluse, whose venom is more potent than that of a rattlesnake, and is toxic to cells and tissues. However, because the bite releases much smaller quantities of poison into its victims, brown recluse bites cause less damage than rattlesnake bites.
Symptoms of Brown Recluse Bites
Brown recluse spider bites may not even be noticed at first as they are often painless. Some people may notice minor stinging such as that felt with a bee sting when bitten by the spider. Symptoms of a brown recluse spider bite develop within eight hours after being bitten and include
- severe pain at the bite site,
- severe itching,
- nausea,
- vomiting,
- fever, and
- muscle pain.
Who Is the Black Widow Spider?
The black widow spider gets its name from the erroneous belief that the female spider kills the male after mating. There are five species of black widow spiders in the US. The southern black widow and the northern black widow are the most common. The spider is medium-sized and about a half-inch long.
Who Is the Southern Black Widow Spider?
The southern black widow spider is one of the two commonly found species of black widow spiders found in the U.S. and can be identified by its shiny, black, globular abdomen with the distinctive red hourglass shape on its underside.
Who Is the Northern Black Widow Spider?
The northern black widow spider doesn’t have the hallmark red hourglass shape on its belly. Instead, it can be identified by a row of red spots (spots may also be yellow or white) down the middle of the upper surface of its abdomen, and two crosswise bars on the undersurface. The spider may be brown or have red legs.
Who Is the Brown Recluse Spider?
Brown recluse spiders are native to the US Midwest and Southeast. It is rare to find them outside these areas. There are 13 other species of spider in the same family that may be falsely identified as a brown recluse.
Who Are the Non-Brown Recluse Spiders?
Spiders in the same family as the brown recluse spider include the desert recluse found in Texas, Arizona, and California, and the Arizona recluse. Bites from these spiders may cause some localized skin disease, but no deaths have been reported from non-brown recluse spiders.
Who Is the Brown Recluse Spider?
Brown recluse spiders are identified by their characteristic violin pattern on the back of the cephalothorax (the part of the body where the legs attach). The base of the violin appears to be at the head of the spider and the neck of the violin points to the rear. Brown recluse spiders are small with one-inch legs, non-hairy, yellow-tan to dark brown in color, and darker legs. Most spiders have eight eyes, but the brown recluse has just six – it belongs to the genus Loxosceles. This eye feature is usually too small for people to see without a magnifying lens .
What Are the Habits of a Black Widow?
Black widow spiders are active at night (nocturnal), and they prefer dark areas. They tend to avoid houses where people live, but they may be found in garages or sheds. Only female black widow spiders bite humans, and they only do so if disturbed.
What are the Habits of a Brown Recluse Spider?
Brown recluse spiders are not aggressive and will only bite if they feel threatened. They prefer dark, warm, dry environments such as attics, closets, basements, barns, and wood piles. Most brown recluse bites occur during the summer. The spider searches for prey at night and rests during the day in its small web, which is usually constructed in corners or crevices.
What Does a Black Widow Spider Bite Look Like?
A black widow spider bite may appear as double fang marks at the site of the bite. The bite is described as feeling like a pinprick, though there may only be a small localized reaction. Blood pressure or heart rate may rise. The severity of the reaction to the bite depends on the age and overall health of the victim. Children and the elderly are usually more seriously affected.
Progression of Black Widow Spider Bite.
Hours after being bitten by the black widow spider, the bite injury will swell. In the case pictured, two days after being bitten the redness and swelling continued past the elbow and down the forearm of the victim. Eight days after the bite, the swelling went down, the bite opened, and the infection was nearly gone.
What Does a Brown Recluse Spider Bite Look Like?
A brown recluse spider bite may appear slightly red and when you look closely you may see fang marks. In most cases, the bite site will become firm and will heal over the following days to weeks with minimal scarring. In some cases, the local reaction will be more severe, with
- redness,
- blistering,
- blue discoloration,
- tissue death, and
- scarring.
Pictured: the bite area swelled to quarter-size within an hour, and within a day continued to swell, turning blue and dark red.
Progressed Brown Recluse Spider Bite (Day Three)
In severe cases, the reaction to a brown recluse spider bite can lead to death of the skin (necrosis) and subcutaneous fat. Pictured: the same person as in the previous slide, after three days, with initial stages of skin necrosis.
Progression of Brown Recluse Spider Bite (Day Nine)
As the reaction to the brown recluse spider bite progresses, severe necrotic lesions with deep, wide borders can result. Pictured: the same person in the previous slides, eight days following the bite. The wound remained open the entire time for the spider’s toxins to drain, and the person needed constant intravenous antibiotics and pain medications.
Progression of Brown Recluse Spider Bite (Day 38)
Eleven days after the brown recluse spider bite a five-inch wide area of dead tissue was removed, and a skin graft was needed. Pictured: skin graft results 38 days after the bite.
Progression of Brown Recluse Spider Bite (10 Months)
Pictured: Ten months after the brown recluse bite, the wound is healed, with scarring.
When Should I Seek Medical Care For a Black Widow Spider Bite?
Seek care immediately following a black widow spider bite at a hospital emergency department. Most doctor’s offices or urgent care centers are not equipped to deal with these types of injuries. Treatment for pain may require narcotic pain relievers and antivenin to counter the effects of the spider venom, which can usually only be found in a hospital setting.
Self-Care Home Treatments for a Black Widow Spider Bite
For minor black widow spider bites, home care treatments are limited. Cold or warm compresses and hot baths may help ease pain. Over-the-counter pain relievers such as acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) may help for mild bites. Folk remedies do not work.
When Should I Seek Medical Care For a Brown Recluse Spider Bite?
If you think you have been bitten by a brown recluse spider, see a doctor immediately or go to a hospital emergency department. If possible, bring the spider to the doctor’s office so the physician can identify the spider to help make the proper diagnosis. Be careful; do not put anyone at risk while attempting to collect the spider.
Are There Self-Care Home Treatments For a Brown Recluse Spider Bite?
Clean the wound area thoroughly with soap and water first, and then seek medical care. Home care is for relief of symptoms only after you have been treated by a doctor. Apply ice to decrease pain and swelling, and take acetaminophen (Tylenol) for pain. Elevate the area above the heart if possible. Avoid strenuous activity which can spread the spider venom through the skin.
Whose Bite Packs a Bigger Sting?
Be cautious of both black widow spiders and brown recluse spiders if bitten. Both can cause painful bites, which can be deadly in some cases. The brown recluse spider bite can cause severe blistering, blue discoloration, and necrotic lesions with scarring. However, the black widow spider bite can cause severe neurological symptoms especially in children or the elderly. Both types of spiders can be dangerous, and you should seek medical attention if bitten by either type of spider.
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