“The only thing we have to fear is fear itself…that and spiders” - Unknown

Dr. Elizabeth Lehto

Introduction

Patients often present to the emergency with a variety of skin findings and worries about spider bites. In the United States, the two spiders that people are often worried about are the black widow (Latrodectus mactans) and the brown recluse (Loxosceles reclusa). Fortunately, there are only about 500 bites a year in the United States and deaths are very rare.

Black Widow Spiders

Black widow spiders (Latrodectus mactans) are found through North America. They make their homes in places that are warm, dark, and dry, such as in basements and garages. They normally only bite humans in self-defense, typically when a hidden spider or its web is disturbed. Only the female is venomous to humans. The female can be identified by its black color and a red hourglass shape or red spots on the abdomen.

The venom lacks human cytotoxic agents, so there is no local tissue injury and little to no local tenderness. The venom causes the release of norepinephrine, Gamma-Aminobutyric Acid, and acetylcholine via exocytosis of synaptic vesicles. It also leads to degeneration of motor endplates which leads to denervation as well as destabilization of nerve cell membranes, which causes a massive influx of calcium into the cells resulting in hypocalcemia.

Signs and Symptoms

The initial bite produces a pinprick sensation that is often unnoticed. Over then next 30 minutes to several hours the bite becomes red and the characteristic halo shaped target lesion appears. This local manifestation is specific for black widow envenomation, but fades after 12 hours and may be missed.

Later, generalized symptoms develop. Patients will have regional lymphadenopathy near the bite site, as well as muscle cramping including pain in the back, chest, or abdomen. Abdominal pain from a black widow bite has been known to mimic appendicitis. Patients may develop a facial grimace or facial swelling. Patients often experience dysautonomia including nausea, vomiting, malaise, sweating, hypertension, tachycardia, and dysphoria.

Untreated patients can have symptoms for up to seven days. Many will have pain, persistent muscle weakness, and sensation of not feeling quite “right” for weeks.

Management

Widow spider bites are rarely life threatening, although envenomation can cause significant pain and require hospitalization.

The cornerstone of management is analgesia, with most patients experiencing pain severe enough to required intravenous opiates. Antibiotics are not routinely recommended. Tetanus should be updated. Most patients will have pain severe enough to require IV opiates. Benzodiazepines can be used to treat muscle spasms.

Symptomatic care also includes adequate hydration and maintenance of severe hypertension. Adequate analgesia usually alleviates hypertension, but if it is persistent nitroprusside or antivenom should be considered.

Latrodectus specific antivenom is available in Australia and Arizona and may be considered in those with sever pain that cannot be controlled by opiate analgesics or those with life-threatening hypertension and tachycardia not controlled with supportive care. Many patients who receive antivenom will have flu like symptoms or a serum sickness like presentation for about 1 to 3 weeks following presentation. One vial is generally sufficient.

Symptomatic patients should be admitted for observation and pain control. Those with convulsions or cardiac compromise should be admitted to the intensive care unit.

Brown Recluse Spiders

Brown Recluse Spiders (Loxosceles reclusa) are brown colored, 1-5 cm long, and have a fiddle-shaped marking on their thorax. This characteristic marking may be absent in many juveniles and spiders who have recently molted. Many harmless spiders have markings that also look like violins.

The most accurate method of identifying a recluse spider involves counting the eyes. While most spiders have eight eyes in two rows of four, recluse spiders have six eyes: a pair in front and a pair on both sides with a gap between the pairs.

Brown recluse spiders hunt at night, typically during the months of April through October. They like to hide in small spaces like closets, attics, old blankets, and shoes.

Signs and Symptoms

Venom contains several enzymes and biologically active substances. Phospholipases D causes most of the clinical findings of loxoscelism, including skin necrosis, platelet disorders, hemolysis, and renal failure.

The initial bite is almost painless, however within a few hours itching, swelling, redness, and tenderness develop over the bite. The lesion progresses to an area of central ischemia to a blue/gray macule surrounded by a pale ring, also know as the red, white, and blue sign.

By the third or fourth day the base becomes necrotic with a central black eschar. Full thickness necrotic ulceration occurs by 1-2 weeks. Lymphadenopathy may be present. The lesion resolves slowly, often over weeks to months.

Cutaneous reaction is more common than systemic symptoms. However, 0.7-1.8% of patents may develop systemic loxoscelism. These patients develop fever, chills, myalgias, diarrhea, nausea, vomiting, and rash. Severe cases can result in disseminated intravascular coagulation (DIC), hemolytic anemia, renal failure, and death.

Management

Management depends on whether or not symptoms are local or systemic.

Local symptoms:

Clean the bite with soap and water
Apply cold packs, heat worsens local symptoms
Affected body part should be in an elevated or neutral position
Pain control: some patients may respond to nonsteroidal anti-inflammatory medications, other may require opioids
Tetanus prophylaxis
Antibiotics are indicated only if signs of infection

Patients with dermal necrosis should receive supportive wound care. Once the lesion is demarcated and clinically stable, debridement and wound care may permit better healing. Early excision is not recommended as it can make the wound worse.

Systemic Symptoms:

Patients with systemic findings including nausea, vomiting, fever, and myalgias should be evaluate for hemolysis, rhabdomyolysis, acute kidney injury, and DIC.

Labs to consider:

Complete blood count
Reticulocyte count
Type and screen with Coombs testing if signs of hemolytic anemia
Complete metabolic panel
Creatinine kinase
Lactate dehydrogenase
Uric Acid if signs of rhabdomyolysis
Urinalysis to look for blood and urobilinogen
Prothrombin time, international normalized ratio, activated partial thromboplastin time
Electrocardiogram if signs of rhabdomyolysis and electrolyte abnormalities

The primary treatment for acute hemolytic anemia consists of blood transfusions for patients with rapidly falling hematocrit or uncompensated anemia. Alkalinization of the urine may be required to prevent hemoglobin-induced renal failure. Antivenom is not available in the United States.

Patients with a rapidly expanding lesion or hemolysis should be admitted. Those with minimal symptoms and reassuring labs can be seen in 24-48 hours by their physician.

NOT RECLUSE

Many patients present with concerns for spider bites and worries that since they did not see a spider the bite must be due to a recluse spider.

The mnemonic NOT RECLUSE can assist in differentiating recluse spider bites from other skin conditions.

N—Numerous: recluse bites are typically a single focal lesion
O—Occurrence: recluse bites typically occur in secluded locations in the home such as the garage rather than outside
T—Timing: lesions appearing from November to March are much less likely to be caused by recluse spider bites
R—Red center: recluse bites typically have a pale enter
E—Elevated: recluse bites are flat or sunken
C—Chronic: lesions presenting longer than several weeks are unlikely to be recluse spider bites
L—Large: lesions >10 cm are uncommon after a recluse spider bite
U—Ulcerates too early (<7 days): suggests infection or pyoderma gangrenosum rather than a recluse spider bite
S—Swollen: significant swelling is not typical for recluse spider bites (apart from bites to the face or feet)
E—Exudative: recluse bites are not moist or exudative (apart from bites on the eyelids or toes)

Summary:

Black widow (Latrodectus mactans): Spiders are black color with a red hourglass shape. Bites classically are a halo shaped target lesion with a pale circular area surrounded by a ring of redness. Systemic symptoms include lymphadenopathy, cramping, vomiting, hypertension, and tachycardia. Many patients require opiates for pain control. Benzodiazepines can be used for spasms. Consider antivenom for patients with severe pain that does not respond to opiates.

Brown Recluse (Loxosceles reclusa): Spiders have a fiddle-shaped marking on their thorax and have six eyes. Lesions are characteristically red, white, and blue in appearance with erythema surrounding an area of blanching around an area of ecchymosis. This is then followed by a necrotic lesion with a black eschar. Systemic symptoms include fever, chills, diarrhea, nausea, vomiting, and rash. Severe cases can result in DIC, hemolytic anemia, and renal failure. Patients with systemic symptoms should be admitted for monitoring.

Elizabeth Lehto, D.O.

University of Louisville | UL · Department of Pediatrics | Doctor of Pediatric Emergency Medicine
Dr. Elizabeth Lehto is a Pediatric Emergency Medicine Attending at Norton Womens and Children’s Hospital. Dr. Lehto attended Midwestern University Arizona College of Osteopathic Medicine and completed her residency and fellowship at the University of Louisville.

References:

Bond G. R. (1999). Snake, spider, and scorpion envenomation in North America. Pediatrics in review, 20(5), 147–151. https://doi.org/10.1542/pir.20-5-147

Hubbard, J. J., & James, L. P. (2011). Complications and outcomes of brown recluse spider bites in children. Clinical pediatrics, 50(3), 252–258. https://doi.org/10.1177/0009922810388510

Parekh, K. P., & Seger, D. (2009). Systemic loxoscelism. Clinical toxicology (Philadelphia, Pa.), 47(5), 430–431. https://doi.org/10.1080/15563650802555515

Vetter, R. S., & Swanson, D. L. (2022, April 28). Bites of recluse spiders. UpToDate. Retrieved July 7, 2022, from https://www.uptodate.com/contents/bites-of-recluse-spiders

Vetter, R. S., & Swanson, D. L., White J. (2021, August 30). Management of widow spider bites. UpToDate. Retrieved July 7, 2022, from https://www.uptodate.com/contents/management-of-widow-spider-bites

Spider Bites

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