Researchers said that spiders in Africa, where humans evolved, presented such a powerful threat to their survival that the ability to spot them became an evolutionary necessity.
This suggests that arachnophobia, one of the most common and crippling of phobias, which affects around 4 per cent of people is something people are born with rather than learn, 'The Sunday Times' reported.
To test how quickly people could pick out a spider even when dealing with a range of other visual stimuli, Joshua New of Columbia University in New York and his colleague Tamsin German asked 252 people to study computer screens containing abstract shapes and data.
They found spiders were spotted fast, even if their shape was distorted.
"A number of spider species with potent, vertebrate-specific venoms populated Africa long before hominoids and have co-existed there for tens of millions of years," said New.
"Humans were at perennial, unpredictable and significant risk of encountering highly venomous spiders in their ancestral environments.
"Even when not fatal, a black widow spider bite in the ancestral world could leave one incapacitated for days or even weeks, terribly exposed to dangers," he said.
"Detection, therefore, is the critical arbiter of success in such encounters - any improvements to the sensitivity, vigilance, reliability and speed of faculties for their detection would have been of significant selective advantage," New added.