many people are terrified of spiders. Why? most spiders are not dangerous - even the scary tarantula, It's true that some of the larger tarantulas can kill small animals like mice or lizards but did you know that no tarantula has ever killed anybody? In fact, only about twenty of the 40,000 species of spider in the world have ever been responsible for a human death, many psychologists believe our fear is a learned behaviour - we see somebody standing on a chair shouting 'spider!' and we copy them. some scientists think our fears go back to the times when we all believed species of insects and spiders carried diseases. Whatever the reasons, it seems that none of us want to admit that our fear of spiders - or arachnophobia - is just, well ... silly.