Clinical Programs: Special Clinical Programs: BROWN RECLUSE SPIDER BITES

A summary based on data compiled from a review of the literature and clinical and laboratory work at Vanderbilt University and the Nashville VA Medical Center

The Spider

Loxosceles reclusa is also known as the brown recluse or fiddle-back spider. It may be light tan to dark brown in color and can be distinguished by a darker, inverted violin-shaped marking on its dorsal cephalothorax. Its long slender legs relative to body size makes it very quick. They measure 1 to 5 cm in length from leg to leg. Crushed spiders may be identified by their three pairs of eyes, unlike some other spider species that have four pairs of eyes. The average lifespan is 543 days for males and 628 days for females. The spider may survive up to 6 months without food or water.

Brown recluse spiders are common to the Southeastern United States, especially in the states of Missouri, Kansas, Arkansas and Tennessee. However, they may be found in any state due to cross-country moving and travel. Most envenomations occur March to October when the spiders are active since they hibernate in winter. The brown recluse prefers dark, dry secluded areas such as woodpiles, attics, storage boxes and piles of clothes. The spiders are naturally shy, nocturnal hunters that bite humans only in self defense. Bites occur most frequently when the spider is trapped against the body by clothing.

The Bite

The classic brown recluse spider bite can be identified by its eccentric or asymmetric shape and by the "red, white and blue" sign which results from reactive erythema, vasoconstriction and thrombosis. The white halo represents ischemic tissue which may later become necrotic. The asymmetric shape is due to gravitational spread of venom attached to erythrocytes. The initial bite is often painless and may go unnoticed. A more intense, local pain, often with pruritus occurs after 6-8 hours. As the lesion progresses, the erythema with central mottling may develop a bleb or blister. The violaceous center may become necrotic within the first 72 hours forming a black eschar. The eschar sloughs at 2-5 weeks leaving an ulcer which may take months to heal (averaging 3-5 months).

Mild Brown Recluse Spider Bite

Moderate Brown Recluse Spider Bite

Severe Brown Recluse Spider Bite

Brown Recluse "Fiddle-Back" Spider


Reported local complications include prolonged wound healing time, scar, persistent pain, functional disability (i.e. hand), loss of tissue (i.e. eyelid), and pyoderma gangrenosum.

Systemic Effects

Reported systemic effects of brown recluse spider bites include fever to 40C, nausea, vomiting, chills, arthralgias, myalgias, weakness, malaise and headache. A generalized pruritic macular eruption (toxic erythema) occurs approximately 48 hours after the initial bite. Mild leukocytosis is a common laboratory abnormality. More severe systemic side effects rarely occur, but are more common in children and in the first 72 hours of the bite. These are usually related to hemolysis and include anemia, thrombocytopenia, DIC, renal failure convulsions and death.

Venom Contents

Sphingomyelinase D: Thought to be the primary dermonecrotic factor and directly causes cell wall lysis.
Hyaluronidase: Spreading factor responsible for gravitational expansion of the wound.
Alkaline phosphatase, 5-ribonucleotide phosphohydrolase and other enzymes: Cause polymorphonuclear cell chemotaxis, platelet aggregation and necrosis.


Putative: Referred patient with subjective diagnosis
  Brown recluse spiders not in area
  Atypical skin lesion
Presumptive: Brown recluse spiders in area
  Compatible lesion which is often early
  Typical clinical course
  Responds to specific therapy
Typical: Brown recluse spiders in area, felt bite, saw spider
  Typical lesion
  Typical clinical course
  Responds to specific therapy
Documented: Brown recluse spider identified
  Characteristic lesions
  Typical clinical course
  Responds to specific therapy

Treatment (RICE DATA)

Rest: Resting the muscle group at the bite site will reduce heat produced by muscle activity. Avoid warm compresses.

Ice: Ice compresses should be applied for 10 minutes out of every 30 minutes since the enzymes in the venom are more active with heat.

Cephalosporins, 1st generation: Antibiotics to cover common skin organisms (i.e. Staphylococcus and Streptococcus). Since secondary infection of the bite site is the most common complication, steroids should be avoided.

Elevation: Elevating the bite site will reduce edema, gravitational spread of the venom and encourage rest.

Dapsone: Dapsone is used for moderate to severe bites, with early signs of necrosis, since it is a neutrophil inhibitor and may prevent some of the other cytokine mediated inflammation at the bite site.

We prescribe 50 mg daily for 48 hours then 100 mg daily and continue until necrosis resolves.

CBC should be evaluated initially then weekly to biweekly to monitor for hemolysis due to the venom and/or dapsone. G6PD (glucose-6-phosphate dehydrogenase) screening is mandatory since dapsone may cause a severe hemolysis in patients with RBC G6PD enzyme deficiency.

Dapsone hemolysis is due to N-hydroxylation of G6PD and may be ameloriated by cimetidine and other agents metabolized by related P-450 enzymes.

Aspirin: Skin necrosis occurs as a result of platelet aggregation and thrombosis. A baby aspirin (81 mg) daily is thought to inhibit some of these venom actions through the cyclooxygenase pathways

Tetanus: Tetanus vaccination should be repeated if not up to date.

Avoid Early Surgery: Early excision and eschar debridement should be avoided because it is impossible to define the extent of venom spread and surgery has been proven to cause delayed wound healing.

Continue therapy until bite activity or ulceration resolves. We follow patients at 1-2 week intervals depending on the severity of the bite and continued ulceration as pyoderma gangrenosum-like lesions may develop.

Key References

Anderson PC. Spider bites in the United States. Dermatologic Clinics 1997; 15(2): 307-11.

Futrell JM. Loxoscelism. Am J Med. Sciences 1992; 304(4): 261-7.

Wasserman GS, Anderson PC. Loxoscelism and Necrotic Arachnidism. J Toxicol-Clin Toxicol. 1983-84; 21(4-5): 451-72.

Wilson DC, King LE Jr. Spiders and spider bites. Dermatologic Clinics 1990; 8(2): 277-86.

Sams HH, Dunnick CA, Smith ML, King LE. Necrotic Arachnidism. J Am Acad Dermatol 2001;44:561-73.

Sams HH, Hearth SB, Long LL, Wilson DC, Sanders DH, King LE. Nineteen documented cases of Loxosceles reclusa envenomation. J Am Acad Dermatol 2001; 44:603-8.