Recent studies of spider phobia have indicated that fear of spiders is closely associated with the disease-avoidance response of disgust.
It is argued that the disgust-relevant status of the spider resulted from its association with disease and illness in European cultures.
The "Disgusting" Spider : The Role of Disease and illness in the Perpetuation of Fear of Spiders; Graham C. L. Davey ; The City University, London
Image caused by the presence or imminence of danger, because there is nothing to fear but birds, ornithophobia and fear itself.