A large portion of spiders are harmless but there are some that can cause dangerous reactions if they bite. Of the 3,000 species of spiders found in North America, the Recluse and the Widow spider species are considered the most dangerous. The venomous bites can be broken out into three groups:
The venom of the Black Widow spider can cause intense pain, elevated blood pressure, sweating, muscle cramps, nausea, and sometimes a rash. The female Black Widow spider, with venom 15 times more toxic than a prairie rattlesnake, is the most dangerous spider in north America.
The venom of Brown Recluse spider, also known as a “violin spider”, can cause lesions, anemia, fever, nausea, vomiting, blood in the urine, rash, and sometimes comas can occur.
The third group includes spiders, the Daddy Longlegs spider for example, possesses venom sacs, but their venom is very mild and virtually non-toxic to humans.