There are about 40,000 known species of spiders in the world.
As of 2008, approximately 40,000 spider species, and 109 families have been recorded by taxonomists, but because of their great ability for hiding, it is believed that about 200,000 species exist. In North America alone, we have at least 3,800 different species. In Ohio, over 520 species have been recorded, but there are undoubtedly many more types to be found here. Most people know that spiders have eight legs; did you know that most types have eight eyes too? In addition to their walking legs, spiders have a pair of short leg-like “palps” located at the front of the body. These palps are used by the males to transfer sperm to the females. Some other animals with eight legs are sometimes confused with spiders. Perhaps the most common animal that is confused with a spider is the “daddy-long-legs” or “harvestmen” which are related to spiders but have only one major body division (spiders have two; a combined head-thorax and an abdomen). Ticks and mites also have eight legs and one major body division. New Zealand has at least 2,500 species, but only 1,300 have a scientific name.
All species are venomous (with the exception of the families Uloboridae and Heptthelidae), but only 40 species are known to be potentially deadly to humans. Key to bite severity: Extremely dangerous: Bite (assuming successful envenomation) may cause death in a healthy adult without emergency medical treatment. Only about a dozen species of spider have venom that is actually harmful to humans, of those only one is a tarantula, all the others are generally small spiders such as the notorious Black Widow or the Brazilian Wandering Spider.
The most common basis for classifying spiders in biological terms is the number of spinnerets that the spider possesses as some kinds possess eight while others are known to have four or six. Another feature is the fangs which are dagger like in some species like tarantulas and funnel web spiders and pincers in species like orb weavers and red back spiders. While most spiders are harmless to humans some like the black widow are venomous, and as such an insect repellent might help when you venture in dusty and hidden places.