Brazilian Wandering Spider
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This spider has the reputation of being the world's most deadly spider. It can be found in Brazil, South & Central America. It also has a leg span of 4-5 inches.
Funnel - Web Spider
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This fellow looks nasty and ready to rumble. It's said that the toxic venom that affects human and primates is only present in the males.
Black Widow
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The Black Widow can be found in all four deserts, American Southwest region. The black widow prefers warmer regions and can be found in other parts of the world. The male of this species are not harmful to humans. However, on the other hand the female as seen above is extremely poisonous to man. If bitten seek medical attention right away.
Brown Recluse: This spider is found mainly in the central Midwestern states and southward into the Gulf of Mexico. If bitten, it depends on how much venom is injected into the victim as well as the sensitivity of the person to the bite.
Below is a great image of this spider.
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This spider as well as the Black Widow can also be found in parts of Canada as well.
Tarantula
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This Spider can be found in the Tropical and Desert regions. Most bites are not life threatening to humans. However, the deep puncture wound can be very painful and infected easily.
Sac Spider
This spider can be found in South Europe.
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There are many kinds of Sac Spiders through out Europe. More than 200 species of yellow sac spiders throughout parts of the world. There's ongoing research into the effects of this spider's bite; in South Africa it is felt they are responsible for 90% of deaths concerning spider bites.
Great pictures. Informative article.