All spiders can be considered deadly to their prey, but from a human perspective, only a small number of species pose any consistent threat to life and limb. Two prime candidates for the most dangerously venomous spiders to people are the “Brazilian wandering spider” (Phoneutriaspp.) and the “Sydney funnelweb spider” (Atrax robustus).
The “Brazilian wandering spider,” from Central and South America, can be very defensive when threatened. These spiders can get fairly large (4-5 inch leg span) and are sometimes encountered in the United States and Canada in fruit shipments, especially bananas. They are frequently misidentified, though, and most turn out to be fairly harmless Cupienniusspecies instead . A bite from a real Phoneutriaspecies can cause tachycardia, hypertension, profuse diaphoresis, hypothermia, salivation, nausea, vomiting, vertigo, visual disturbances, priapism (especially in boys less than 10 years old), and very rarely death within 2–12 hours.
The “Sydney funnelweb spider,” from Australia, is a fairly large spider with long, strong fangs and potent venom. It has attracted a lot of attention since it has been blamed for 14 deaths since 1927. Bite symptoms include local pain, salivation, lachrymation, skeletal muscle fasciculation and disturbances in respiration, blood pressure, and heart rate… followed by severe hypotension or death due to respiratory and circulatory failure. The males of this species, which normally inhabit funnel-like webs, wander in search of mates, taking them through suburbs and putting them right in the path of people. Confronted with a potential predator, Atrax doesn’t back down, either, instead often rearing up and striking aggressively with fangs erect. They can easily pierce the fingernail of an infant, or punch through the average shoe. However, surprisingly few bites from this spider even require antivenin, let alone put a person at death’s door. Since antivenin was developed in the early 1980s, not one single death has occurred from a “Sydney funnelweb spider” bite. Even before that, less than 1% of those bitten actually died. In fact, statistics tend to show that “deadly” species are among what one could call a spider myth. You have more to fear from lightning strikes. That is not to say that being bitten by a spider like an Atrax or a Latrodectus(black widow) is a pleasant experience. Far from it, and you should take simple precautions to avoid potential bites.
Original article from spiderid.com