| Initial bite symptoms | Moderately to severely painful; little or no surrounding inflammation | Painless or minimally painful; localized inflammation that subsequently spreads |
| Presumed mechanism of envenomation | Massive presynaptic discharge of all autonomic neurotransmitters | Local cytotoxicity with subsequent ulcerating dermonecrosis |
| Predominant toxin | α-Latrotoxin | Sphingomyelinase D |
| Potential for systemic toxicity | Present; usually atypical and rarely full-blown (latrodectism) | Present but rare (loxoscelism) |
| Incubation period from bite to systemic toxicity | Rapid (i.e., 30 minutes to two hours) | Delayed (i.e., three to seven days) |
| Most common signs of systemic toxicity | Muscular spasm and rigidity beginning at bite site and spreading proximally to abdomen and face; rebound tenderness mimicking acute appendicitis is possible. | Arthralgias, fever, chills, maculopapular rash, nausea, vomiting |
| Potential associated signs of systemic toxicity | Arthralgias, bronchorrhea, regional or generalized diaphoresis, fever, hypertension, hyperreflexia, regional lymphadenopathy, nausea, vomiting, paresthesias, priapism, ptosis, restlessness, salivation | Febrile seizures, hemoglobinuria, myoglobinuria, acute renal failure |
| Outcomes of most bites | Resolution of all manifestations over two or three days; death rarely occurs | Most necrotizing ulcers will heal over one to eight weeks with a 10 to 15 percent incidence of major scarring. One study found no deaths in 111 patients with entomologist-confirmedLoxosceles reclusa bites.15 |