Arachnophobia can be triggered by the mere thought of a spider or even by a picture of one, in some cases. Many people who fear spiders feel panic entering a situation where spiders may be present. Symptoms include excessive sweating, rapid breathing, a quickened heartbeat, nausea and dizziness.

Some arachnophbics will, on entering a room, search it for a spider. If they find one they will monitor its progress very thoroughly. Others will do all in their power to distract themselves to avoid seeing the spider.

There are historical and cultural reasons for arachnophobia. In the Dark Ages spiders were commonly considered to be a source of contamination of food and water. They were believed to be the cause of the Bubonic Plague (though in reality rat-fleas were in fact the true culprits). This misplaced fear has been passed down since the 10th Century.

Often the fear is caused by a frightening incident in earlier life. Sometimes people have the misconception that such a startling event has to be a memorable ordeal. Yet many don't even recall the events that led to their phobia. The mind can create a phobia based on a split second of panic.