Bites of spiders belonging to the genera Latrodectus, Phoneutria, and Loxosceles can cause severe, even fatal, systemic poisoning in humans. The most numerous of the venomous spiders are of the genus Latrodectus.
Why Is This Genus So Dangerous?
The venom of spiders in the genus Latrodectus (which includes the American black widow spider) and in members of the genus Phoneutria is a nonhemolytic, noncytotoxic neurotoxin that produces diffuse central and peripheral nervous excitement, autonomic activity, muscle spasm, hypertension, and vasoconstriction in humans. Other symptoms may include abdominal rigidity, intense pain, paresthesia, headache, sweating, nausea, and facial blood vessel congestion.
What Other Types Of Spiders Are Dangerous?
The venom of spiders of the Loxosceles genus (which includes the brown recluse spider) is a mixture of hemolysin and cytotoxin that causes ischemic necrosis at the site of the bite. The bite is often relatively painless, and the lesion is initially 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.
What Ocular Effects Can The Venoms Produce?
The ocular effects of these spiders' venom include edema, gangrene, necrosis, ptosis, and purpura of the lid; conjunctivitis; subconjunctival hemorrhages; pupil constriction; retinal cyanosis; and visual disturbance.
