Back in 2007, Popular Science reported on a fascinating study:

• In a study exotic dancers made $70 an hour in tips when they were at their most fertile.
• This was double the $35 an hour they made when they were menstruating – or at their least fertile.
• Researchers suggested that this was because women were more flirtatious at peak fertility.
• Those who took birth control averaged $37 an hour, and didn’t see variations in their wages.
• This led researchers to lament the thousands of dollars that strippers on birth control lost every year.
• The scientists also recommended that girls in the industry schedule more shifts around specific times in the calendar.

Read more here.

Source: Popular Science