The most numerous of the venomous spiders are of the genus Latrodectus . Other symptoms may include abdominal rigidity, intense pain, paresthesia, headache, sweating, nausea, and facial blood vessel congestion. The bite often is relatively painless, and the lesion initially is surrounded by a bluish-white halo of vasoconstriction that may later develop extensive gangrene. Tarantulas, or wolf spiders, of various genera, including Lycosa and Phidippus , also may cause necrosis and ulceration in humans. The genera Latrodectus, Phoneutria, and Loxosceles can cause severe even fatal systemic poisoning in humans.
Spider bites are more frequent in males than in females.
The genera Latrodectus, Phoneutria, or Loxosceles may cause systemic reactions. See Pathophysiology . For mild lesions, broad-spectrum antibiotics and antihistamines are used. It is important for the patient to capture and bring in the spider, if possible, to help determine the necessary treatment. Poisoning by spiders of the Latrodectus genus may require intravenous calcium gluconate alternating with methocarbamol to relieve muscle cramps.