In what is surely one of the strangest surveys of the month - if not the year - scientists have found that women are better at detecting snakes just after they have finished their periods.

The research, which examined our inbuilt instincts for survival, tested 60 healthy women of child-bearing age at three different phases of their cycle.

Subjects were shown nine pictures of flowers, one of which also included a snake. They were timed on how quickly they spotted the serpent.

Women in the so-called luteal phase of their menstrual cycle, or the stage that immediately follows ovulation, identified the snakes the quickest.

Scientists at Japan's Kyoto University said the results indicate humans have an innate "fear reflex" triggered by threatening stimuli such as snakes.

Among women, this mechanism appears to be affected by hormone levels and may be more potent at a time when they could be pregnant - and so more protective because of their foetus.

"It could contribute to women's ability to increase their vigilance towards biologically relevant threatening stimuli around themselves during this period of possible pregnancy," the study concluded.

Results were published in the British journal Scientific.

Women 'spot snakes best after ovulation'