The Telegraph reports that ISIL fighters in their peculiar ideology believe that they will be denied heavenly rewards as martyrs if they are killed by a woman:
The increasing number of female soldiers taking to the front line against extremists of the Islamic State in Iraq and the Levant (Isil) is sowing fear in their ranks that they will be denied their prize in paradise, according to Ed Royce, who chairs the US House International Relations Committee.
"These Isil soldiers apparently believed that if they were killed in battle, they went to paradise as long as they were killed by a man," he told The New York Post, citing reporters of Kurdish female fighters laughing as they repelled attacks by the extremist group.
Also, this documentary makes the same point at about the 16:00 mark:
For an IS fighter to be killed by a woman is the ultimate disgrace. They’ll never make it to paradise.
So that brings up an idea for future airstrikes against Daesh positions. The US has accepted female combat pilots since 1993 (thanks, Bill).
Let them think about that in their bunks!