Fans of the TV series Sex and the City may not be surprised, but scientists have found women are prone to bitchiness when they are on the hunt for a man.
It is because females become far more critical of the looks of potential rivals when they are at their most fertile, say researchers.
This use of 'indirect aggression' to denigrate potential rivals is designed to boost their chances of finding a 'good man'.
And the phase of cattiness can last as long as ten days each month, psychologists have found.
'When women are at their most fertile, they'll pay more attention to each other's appearance,' said Maryanne Fisher, of York University, Toronto.
'There can be more catty behaviour, there will be more gossiping, nit-picking and spreading of nasty stories.
'You might see two women in a pub and one might say to the other, "Oh my God, look at her, she's so ugly" or "your hair is such a mess". That is an example of a competitive strategy.' 
- http://www.thisislondon.co.uk/news/article-9201473-details/When+women+get+their+claws+out/article.do [↩]