1. Elizabeth Báthory

2. Belle Gunness

3. Amelia Dyer

4. Mary Bell

5. Delphine LaLaurie

6. Jane Toppan

7. Gwen Graham and Cathy Wood

8. Genene Jones

9. Júlia Fazekas and the Angel Makers of Nagyrév

10. Aileen Wuornos

11. Leonarda Cianciulli

They might be less common, but they're no less scary.
Elizabeth Báthory, a Hungarian Countess at the turn of the 16th century, is considered by many to be the most prolific female serial killer of all time: while she is publicly accused of killing 80 young girls, some speculate the number is as high as 650. Báthory lured her victims to her castle under the guise of well-paid servant work or courtly etiquette lessons. Some witnesses claimed they saw her biting flesh off her victims, and others claimed she drank their blood; these allegations (though unproven) earned her the nickname "The Blood Countess."
Norwegian-American Belle Gunness was responsible for killing 40-plus people in the very early 20th century. Most were suitors and husbands; Gunness' motive was thought to be the collection of life insurance policies and other sources of wealth. After killing her first two husbands, Gunness placed a personals ad that would attract several of her later victims: "Personal — comely widow who owns a large farm in one of the finest districts in La Porte County, Indiana, desires to make the acquaintance of a gentleman equally well provided, with view of joining fortunes ... Triflers need not apply."
Gunness allegedly faked her own death in an arson set in her home; the headless body of a woman dressed in her clothing was later discovered in her bed. (Her dead children were also found in theirs.) Several witnesses who saw the body said there was no way it could be hers (Gunness was 6'0" and 200 pounds), but dental records later "confirmed" it. However, a hired hand of Gunness' said that she'd placed her own false teeth in the corpse's head (which she'd dressed as herself), and escaped by train. Gunness was reportedly sighted around the United States for decades afterward, but her ultimate fate is unknown.
Wikipedia has given Amelia Dyer the very dubious superlative "most prolific baby farm murderer of Victorian England." Confirmed killer of six babies, Dyer is the attributed killer of between 200 and 400. Dyer provided lodging for women who became pregnant "illegitimately" in exchange for a fee. Early on, like other baby farmers, Dyer either procured adoptions for the babies or allowed them to die of malnutrition. At some point she began murdering them. Dyer was caught in 1879, sentenced to six months of hard labor on the charge of "neglect," and released — at which point she resumed murdering babies. She was caught again in 1896, pled guilty, and was hanged.
Mary Bell was just 11 years old when she strangled two young boys (3 and 4 years old) to death in Scotswood, England. After killing the younger of the two victims, Bell reportedly returned to the scene and carved the letter "M" into the boy's stomach with a razor, among other mutilations. Bell was released from prison in 1980 at the age of 23, and has lived under court-protected anonymity ever since. In 1998 Bell collaborated with author Gitta Sereny on a book about her life called Cries Unheard: The Story Of Mary Bell.
Delphine LaLaurie, known as Madame LaLaurie, was a Louisana-born socialite and serial killer of slaves in the early 19th century. Despite outward, public politeness to black people, rumors of LaLaurie's unusually cruel mistreatment of slaves were widespread. After a fire in her home, bystanders entered the residence in order to make sure everyone was evacuated. It was then that they encountered an apparent torture chamber, where several slaves were hung by the neck. After her house was attacked by an angered mob, LaLaurie fled to Paris. She is suspected to have been involved in the torture and murder of hundreds of black slaves.
Jane Toppan confessed to 31 murders in 1901. Toppan was a trained nurse who used her patients as involuntary subjects in self-directed tests involving morphine and atropine. Toppan concocted many of the patients' conditions herself, often creating fake charts to "monitor" their progress. She later confessed to getting a sexual thrill from being with patients near death. After being fired, she began a poisoning spree, killing her landlords and her foster sister. In an attempt to woo the foster sister's widowed husband, she poisoned him in order to nurse him back to health. After poisoning an elderly charge, Toppan was arrested and confessed. She was found not guilty by reason of insanity, and committed to the Taunton Insane Hospital until she died at 81.
Gwen Graham and Cathy Wood met at the Alpine Nursing Home, where they worked as nurse's aides. The two became girlfriends and together conspired to smother five elderly patients, allegedly as part of a "love bond." The couple broke up when Graham began dating another woman and moved with her to Texas. In 1988 Wood's ex-husband (whom Wood had told about the murders) went to the police. During investigations, Graham and Wood each would accuse the other of being the crimes' primary motivator, as well as the manipulative half of the couple. Graham was found guilty of five counts of murder and sentenced to five consecutive life sentences. Wood was charged with one count of second-degree murder and sentenced to 20 years, as part of a plea bargain. She is expected to be released in 2021.
Genene Jones was a pediatric nurse who is the confirmed killer of one infant, but the suspected killer of upward of 60 infants between 1971 and 1984. Jones injected her patients with drugs like digoxin and heparin in order to induce sickness, so that she might revive them and be praised. However, many of the injected infants did not survive. When the hospital where Jones worked (Bexar County Hospital) noticed that a statistically unlikely number of babies died under her care, they asked her to leave rather than undertake an investigation. Jones resumed her mission at her next hospital, and was ultimately charged with poisoning six children there. Jones is held in Texas, and is thought to be the inspiration for Annie Wilkes in the Stephen King novel Misery.
Led by a midwife named Júlia Fazekas, the Angel Makers of Nagyrév were a group of women living in the Hungarian village of the same name who, between 1914 and 1929, poisoned an estimated 300 people. Fazekas encouraged women who wanted to escape undesirable home lives (whether unwanted returned husbands or unwanted children) by poisoning their family members. Many of the women were wives of WWI soldiers and had taken foreign lovers in their husbands' absence. Fazekas is alleged to have said, "Why put up with them?"
Aileen Wuornos, famously portrayed by Charlize Theron in the 2003 film Monster, killed seven men in Florida between 1989 and 1990. Wuornos worked as a prostitute, and claimed that the murders were done in self-defense. Her first victim was a convicted rapist. Wuornos was arrested on an outstanding warrant in 1991, and confessed to the murders with the encouragement of her ex-girlfriend, who wanted immunity from prosecution. Wuornos was sentenced to death, and executed in Florida in 2002.
Leonarda Cianciulli was an Italian woman who killed three women between 1939 and 1940, and turned their corpses into soap and teacakes. In a book she wrote titled An Embittered Soul's Confessions, Cianciulli described her first murder:
"I threw the [body] pieces into a pot, added seven kilos of caustic soda, which I had bought to make soap, and stirred the whole mixture until the pieces dissolved in a thick, dark mush that I poured into several buckets and emptied in a nearby septic tank. As for the blood in the basin, I waited until it had coagulated, dried it in the oven, ground it and mixed it with flour, sugar, chocolate, milk and eggs, as well as a bit of margarine, kneading all the ingredients together. I made lots of crunchy tea cakes and served them to the ladies who came to visit, though Giuseppe and I also ate them."