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Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023
| Contributor Information
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Image from Naidu DK, Ghurani R, Salas RE, Mannari RJ, Robson MC, Payne WG. Eplasty. 2008 Aug 28;8:e45. PMID: 18820724. [Creative Commons (CC) Attribution License.]
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
Some spider species can inflict serious injury, as demonstrated by the above image of osteomyelitis of the mandible resulting from the bite of a brown recluse spider (Loxosceles reclusa). Spider venom, a sophisticated cocktail of neurotoxins, amines, and enzymes,[1] can contain up to 3000 different molecules[2] and can in some instances cause significant morbidity or even death. In most cases, however, it has no substantial effect on humans, with fewer than three deaths from spider bites estimated to occur annually in the United States, most often in children.[3]
In the United States, only the black widow and brown recluse are known to be harmful to humans.[4,5]
Inset image from Wikimedia Commons | Br-recluse-guy. [Public domain.] Main image from the Centers for Disease Control and Prevention (CDC). [Public domain.]
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
Recluse Spiders
A bite from the brown recluse spider (L reclusa) is shown.
The brown recluse, or violin spider (inset), has six eyes as well as a characteristic fiddle-shaped pattern on its cephalothorax. Its range extends from central Texas to Tennessee and from southern Illinois to the Florida Panhandle.[6] Its habitat includes secluded, dry, sheltered areas (eg, woodpiles, spaces between walls, disused storage areas, cellars/attics). The brown recluse spider is not aggressive toward humans, but it will bite if it feels threatened[4]; such bites can occur, for example, when the spider has concealed itself in clothing or upholstery.
The Mediterranean recluse spider (L rufescens) is also established in North America. It has no history of medical significance.
Image courtesy of Medscape | Dale Losher.
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
A confirmed brown recluse bite on the thigh is shown. The patient's physician drew a circle around the area of initial swelling, with bite-related blue and dark red markings on the skin exceeding that area within the first day.
Brown recluse venom is cytotoxic and hemolytic, and the spider bite can induce loxoscelism, an intense inflammatory response leading to local and systemic complications.[7-10] Systemic symptoms include morbilliform rash, fever, chills, nausea, vomiting, arthralgia, hemolysis, disseminated intravascular coagulation, renal failure, seizures, acute hemolytic anemia, and coma.[7,8,11,12] Cutaneous loxoscelism leading to necrosis is more common in fatty areas, such as the thigh, because recluse venom has a dynamic detrimental effect on adipose tissue.[10,13]
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
The bite of the Chilean recluse spider (L laeta) is shown above. In South America, this spider as well as its congeners, L gaucho, L yucatana, and L intermedia, are also known to cause loxoscelism.[13,14] A protective vaccine against loxoscelism, based on the venom of L intermedia, has been effective in trials involving mice and rabbits.[15]
Image from Wikimedia Commons | Steve Ryan-juniorvelo. [CC Attribution-Share Alike 2.0 Generic License.]
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
Widow Spiders
Black widow spiders can usually be identified by the classic red hourglass shape on the underside of the abdomen (shown).
Widow spiders (genus Latrodectus) include the black widows (L mactans, L hesperus, L variolus), brown widow (L geometricus), and red-legged widow (L bishopi).[8] Widow spiders are common and abundant in the southern and western United States.[7,8,16] The males and juveniles do not bite; females tend to be stationary and unwilling to bite unless provoked.
Widow spider venom, which contains an alpha latrotoxin, causes neurologic and autonomic dysfunction.[7,8] Reactions to envenomation are typically minor,[17,18] but serious symptoms can include severe abdominal cramping, hypertension, nausea, perspiration, and urinary retention.[19] Initial research from Albania suggests higher summer temperatures correlate with higher potency of widow spider venom.[20]
Image courtesy of David Oconnor.
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
Another widow spider, the redback spider (L hasselti), is found throughout Australia. This species, which has a red dorsal stripe, is related to the American black widow. The female redback spider is responsible for all significant bites.[7,21]
Redback spider bites cause local pain and erythema in over 80% of patients and can be identified by the presence of two fang marks, like those seen in the above image. The bites can go on to involve an entire limb via lymphatic drainage in the axilla or groin.[22] Systemic symptoms include nausea, vomiting, abdominal pain, headache, and migratory arthralgias.[7,21] In one third of cases, fever, hypertension, tachycardia, weakness, fasciculations, and paralysis may develop. Rare complications include myocarditis and rhabdomyolysis.[7]
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
False Widow Spiders
The common false widow (or rabbit hutch) spider (Steatoda bipunctata) is shown.
False widow is a name given to a number of spiders that belong to the genus Steatoda. Although often mistaken for widow spiders, false widow spiders lack the red hourglass pattern on the underside of the abdomen, often have distinctive coloring, and are usually smaller.[23] In the contiguous United States, false widows are found in almost every region.
The bite of the false widow is generally less severe than that of the black widow, although the two share many important venom components.[24] It can produce a condition known as steatodism, the symptoms of which include moderate to intense pain, generalized malaise, pruritus, and local skin blistering.[23,25]
Image courtesy of Arlo Pelegrin.
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
Wandering Spiders
Four of the eight eyes of wandering spiders are arranged in a square, as pictured in Phoneutria boliviensis (above).
Wandering spiders belong to the tropical and subtropical family Ctenidae. The genus Phoneutria contains spiders that are commonly thought to be among the most venomous in the world[26-29]; considered aggressive, they roam the jungle floors of Central and South America.[26]
A review of confirmed Phoneutria bites showed that 90% of the victims had mild reactions,[28] but this spider can potentially cause serious injury. The venom of the Brazilian wandering spider (P fera), which contains at least 41 neurotoxins,[29] results in paralysis and asphyxiation; serotonergic effects that lead to intense pain and inflammation are also produced by this venom.[26,30]
Image courtesy of Arlo Pelegrin.
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
Yellow Sac Spiders
Yellow sac spiders (family Cheiracanthiidae) have in the past been reported to be capable of causing a cutaneous reaction known as necrotic arachnidism. However, review of the presentations of confirmed sac spider bites has not corroborated the alleged seriousness of their venom and suggests that these spiders may have been erroneously elevated to the status of dangerous animals.[31,32] Yellow sac spiders are common in North American homes, especially in kitchens, bathrooms, and other rooms with plumbing. If cornered, crushed, or otherwise provoked, they can bite, causing moderate to intense pain. Bites are typically followed by a rapid recovery.[32,33]
Image courtesy of Arlo Pelegrin.
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
Wolf Spiders
A wolf spider in the genus Pardosa is shown carrying her young.
Despite widely promoted mythology, wolf spiders (family Lycosidae) are extremely reluctant to bite, with most species being harmless. A diverse group found throughout the world, these spiders particularly occur in grasslands and meadows.[34] They are usually well-camouflaged and typically have dark body markings such as stripes.[34,35] At close range, wolf spiders are identified by their low-to-the-ground stance and the four large eyes visible on the top of the head. A review of 45 confirmed wolf spider bites showed that victims experienced pain of short duration and that systemic effects were rare (7%).[36,37]
Image courtesy of Michael Doe, Project Maratus.
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
Jumping Spiders
The peacock spider (Maratus madelineae), a species of jumping spider, is shown.
Jumping spiders (family Salticidae) are ubiquitous, living everywhere that humans do. They frequently prey on pests. These spiders are typically smaller than a thumbnail and are easily distinguished by their large eyes, square carapace, and confident jumping.
Jumping spider bites are rare because the spider will always choose to escape rather than stand and fight. Bites are usually painful, erythematous, and urticating but do not cause severe symptoms.[38] In comparative cytotoxic assays, jumping spiders have been shown to possess highly potent venom.[39]
Image courtesy of Kevin Wright.
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
Tarantulas
The bite of a curly hair tarantula (Tliltocatl albopilosus) is shown, along with the spider itself.
Tarantulas (family Theraphosidae) are among the world's largest spiders (4.75 inches [12 cm] long; leg span up to 11 inches [28 cm]) and can be found in tropical, subtropical, and arid regions.[40]
The bite of a tarantula is usually very painful but not dangerous.[41-44] The most common reactions are muscle spasms[45] and a local histamine response with edema and erythema, much as with a bee or wasp sting.[40-42] Envenomation by the genera Poecilotheria and Heteroscodra has been reported to cause particularly intense muscle spasms.[13] The venom of Haplopelma hainanum, a popular pet species, can induce inflammatory skin lesions.[41]
Image from Wikimedia Commons | Morkelsker. [Public domain.]
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
Critically endangered in the wild, the Gooty tarantula (Poecilotheria metallica, shown), an Old World species, has become a popular and highly prized trade commodity, despite having a medically significant bite.[46]
Old World tarantula species are usually more aggressive, and their venom is thought to be more potent than that of New World species. However, many spiders, including tarantulas, can choose to inflict a "dry bite" in order to conserve physiologically expensive venom.[2] In such cases, only mechanical damage is incurred. Many Old World tarantula species possess venom that has shown promise in medical applications, such as pain management.[47]
The popularity of tarantulas among collectors has led to an increase in first-time reports of bite effects from a variety of taxa.[48,49]
Image from Dreamstime | Armando Frazão.
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
Funnel-Web Spiders
Australian funnel-web spiders (family Atracidae), particularly Atrax robustus (the Sydney funnel-web spider, shown in the attack position), are, like members of Phoneutria, considered to be among the most venomous spiders in the world.[50,51]
Funnel-web spider bites are very painful but usually only lead to mild or local neurotoxic effects. In severe cases, nausea, vomiting, diaphoresis, salivation, piloerection, lacrimation, pupillary changes, hypertension, tachycardia, pulmonary edema, fasciculations, spasms, massive sympathetic and parasympathetic autonomic stimulation, oral paresthesia, and coma may occur.[52] The venom of funnel-web spiders (named for the funnel-like burrows they build) contains a delta atracotoxin (robustoxin), which is a polypeptide neurotoxin.[8,50,52,53]
The common name "funnel weavers" refers to the harmless Northern Hemisphere family Agelenidae.
Medically Significant Spider Bites: Which to Watch Out For
Lars Grimm, MD, MHS | July 25, 2023 | Contributor Information
Mouse Spiders
A red-headed mouse spider (Missulena occatoria) is shown.
Mouse spiders (genus Missulena, family Actinopodidae) are sometimes mistaken for Australian funnel-web spiders.[54,55] Members of this genus are found mostly in the coastal and drier areas of Australia, but one species lives in Chile. Mouse spiders do not occur in tropical rainforests. The spiders can be distinguished by their squat build, widespread eyes, wide head, and glossy carapace. Unlike funnel-web spiders, mouse spiders are more likely to produce dry bites, without injection of venom.[55] When envenomation does occur, it is nearly as serious as that from the funnel-web spider.[54,55] Funnel-web spider antivenin is an effective treatment.[54]
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Author
Lars Grimm, MD, MHS
Associate Professor
Department of Diagnostic Radiology
Duke University Medical Center
Durham, NC
Disclosure: Lars Grimm, MD, MHS, has disclosed no relevant financial relationships.
Editor
Richard S Krause, MD
Clinical Assistant Professor (retired)
Department of Emergency Medicine
The State University of New York University at Buffalo
Jacobs School of Medicine and Biomedical Sciences
Buffalo, NY
Disclosure: Richard S Krause, MD, has disclosed no relevant financial relationships.
Reviewer
Arlo Pelegrin, MSc
Professor of Biology
Community College of Aurora
Aurora, CO
Disclosure: Arlo Pelegrin, MSc, has disclosed no relevant financial relationships.
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