Spiders are found worldwide on every continent except for Antarctica and have become established in nearly every ecological niche with the exception of air and sea colonization. As of 2008 taxonomists have recorded approximately 40,000 spider species and 109 families.
Most spiders will only bite humans in self-defense and few produce worse effects than a mosquito bite or bee sting. Most of those with medically serious bites such as recluse spiders and widow spiders are shy and bite only when they feel threatened but this can easily arise by accident.
Funnel web spiders’ defensive tactics are aggressive and their venom, although they rarely inject much, has resulted in 13 known human deaths. There were approximately 100 documented deaths from spider bites in the 20th century compared to 1,500 deaths from jellyfish stings. Many alleged cases of spider bites may represent incorrect diagnosis, which would make it more difficult to check the effectiveness of treatments for genuine bites.