Are there female Serial Killers?

There has been much debate in the true crime community about why there are more male serial killers than female, however, this is not necessarily the case, it is possible that the methods women use to kill are less violent, due to the pathology of men and women. Male serial killers are mainly motivated by sexual impulses and female serial killers by gain, the black widow trope
 
 This episode will cover two female serial killers and will therefore be slightly longer than the usual episode. We will start with a case that goes against the grain of female serial killers, killing less violently and for gain, we will start with Darya Nikolayevna Saltykova an 18th century Russian Noble Woman, that plead guilty to torturing and killing 138 serfs at her estate.