Spiders occasionally bite humans. Although 98-99% of spider bites are harmless, more rarely, the symptoms of their bites can include necrotic wounds, systemic toxicity, and in some cases, death. Four genera are known to have potentially lethal bites. In almost all cases of spider bite, the chief concern is the spider's venom. Spiders regarded as dangerous possess venom which is toxic to humans in the quantities which can be delivered...