In Russia, Chechen female suicide bombers known as the Black Widows have struck devastating blows in past weeks, reportedly carrying out attacks on airliners and near a Moscow subway station, and joining a hostage-taking at a school in the town of Beslan.

In Israel, Palestinian women have blown themselves up in assaults that have killed more than 35 Israelis and wounded hundreds of others.

In Iraq, genetic engineer Huda Salih Mehdi Ammash is suspected of taking a high-profile role in rebuilding Baghdad's biological warfare capacity. She is imprisoned along with microbiologist Rihab Taha, said to be a former director of a bacterial and biological warfare program aimed at mass killing.

The participation of women and, sometimes, teenage girls in an increasing number of deadly acts has horrified the international public, and a wave of revulsion has rolled through the media at female violence in its most ruthless form.

Yet, the extent and causes of women's violence are uncertain and remain unpredictable in a world in which aggression has been the province of men, and violent women considered mentally unbalanced or possessed by unimaginable evil.

Those who are now studying female violence agree that it has long been a neglected issue. Until the 1960s, it was almost taboo, surfacing mostly as the subject of sensational news reports.

More recently, some feminists played down female violence, calling it a reaction to the abuse of women by men throughout the world. Others, like Valerie Solanas of SCUM (Society for Cutting Up Men) — who shot and wounded Andy Warhol — gloried in violent revenge and aggressive female self-expression, earning themselves the label of the lunatic fringe.

But the appearance of women as terrorists has focused attention on the seriousness of female violence, and shocked onlookers are asking why and how such appalling crimes are being committed by those once known as the gentle sex.

The shock is not only registering in the West. In Muslim countries, where women are often expected to assume more passive roles than men, taking up arms is unusual. In Chechnya, women were traditional peacemakers, and an ancient custom decrees that a man seeking blood revenge will halt an attack on his enemy if a woman throws her headscarf on the ground.

But the images of Chechen and Palestinian women who have given up their lives to attack innocent people indicate that the facts are contradictory.

"It's particularly startling because, in general, women's suicide rates are much lower than men's," says Patricia Pearson, author of an award-winning study of female aggression, When She Was Bad: Violent Women and the Myth of Innocence. "It's not the kind of behaviour we expect from women."

Widely circulated Internet photos of Reem Saleh Riyashi, the first female suicide bomber trained by the militant Hamas organization, highlight the stark contrast of roles: A sweet-faced woman holds a smiling toddler in one arm and a machine gun in the other. One morning in January, Riyashi left her two infants with her husband, strapped on an explosive belt and blew herself up at a border crossing on the Gaza Strip, killing four Israelis.

Earlier, six other Palestinian women from widely different backgrounds also killed themselves in suicide attacks, starting in January, 2002. They include Hanadi Jaradat, a 29-year-old lawyer with telegenic looks and an upcoming marriage, Wafa Idris, an impoverished Palestinian refugee who was deserted by her husband, and Dareen Abu Eishi, an extremely religious woman who had lost two relatives in clashes with Israeli troops.

The women themselves have left few clues to their states of mind, and reports of the rare ones who have surrendered are dubious because of their need to gain the favour of the authorities who detain them.

In Russia, 23-year-old Chechen Zarema Muzhakhoeva — who says she deliberately bungled a suicide bombing at a café in central Moscow in July, 2003 — told Russia's daily Izvestia a surprising story of financial ruin and domestic crime. When her husband was killed by business associates, leaving her unable to support an infant daughter, Muzhakhoeva said, she robbed her grandparents of about $765, then sought money to repay them and reclaim the child from her in-laws' care.

Hearing that a suicide bomber's family would receive $1,000, she promptly volunteered. But the leader of the training camp tried to discourage her because he disapproved of killing oneself for money rather than religious principles.

But she rejected his offer of marriage to a fighter who would support her, because "I wanted to die — not sit in the woods like a rat."

While money was allegedly the motivating factor in Muzhakhoeva's decision to turn to violence, Israeli analysts say that the involvement of Palestinian women in deadly suicide attacks fall into two main categories.

"Most of them were pushed to the fringes of Palestinian society for violating a Muslim conservative rule of conduct obligatory for Palestinian women," says a recent report from the Intelligence and Terrorism Information Center at the Israeli-based Center for Special Studies.

"For some women, the motive was also vengeance for the deaths of relatives and loved ones killed in the course of the ongoing Palestinian violent confrontation with Israel."

Dr. Meir Litvak of Tel Aviv University says that the growing phenomenon of women suicide bombers is also due to the devaluation of women that makes them targets for opportunistic male militant leaders.

"They are exploiting the personal frustrations and grievances of these women for their own political goals, while they continue to limit the role of women in other aspects of life," Litvak told the daily Guardian.

In Chechnya, many of the women who joined the Black Widows suicide squad have lost relatives during the 10-year war with Russia that has left few Chechens untouched by tragedy.

"You have had a bad day," a female hostage-taker told one of her Russian captives during a dramatic siege of a Moscow theatre. "I have had a bad 10 years."

The Chechen terrorist attacks, as well as those in Israel, appear to be entirely directed by men. But the idea that women are passive pawns of ruthless warlords may be a myth, says British terrorism analyst Rhiannon Talbot, a law lecturer at the University of Newcastle.

"In many cases, women are indignant when they're seen as pawns of men," she says.

"They may be even more committed than their male colleagues, because they have more social hurdles to overcome. But in the West, they are often tied to the conventional stereotype of reacting to male violence."

Although many people today are shocked by such deliberate female violence, Jeannine Davis-Kimball, a California-based archaeologist and ethnographer, says there is little new about it.

"Women's desire to protect their families and their societies is as strong or stronger than men's," she says.

"From that point of view, we shouldn't be surprised by it."

In an extensive archaeological investigation in Russia and Central Asia, Davis-Kimball found evidence of warrior women who fought alongside men and played an aggressive part in the nomadic Central Asian tribes of the Sarmatians and Sauromatians in 600 B.C. to 400 B.C.

Her book, Warrior Women, documents the fact that a passive, domestic role was not always the norm for females.

"I think that the same thing is true of North America and the early plains settlers. Those women were left alone much of the time and they had to be able to fire a gun," she says.

Historically, women as warriors were first noted by the Greek historian Herodotus, who described bloodthirsty females who cut off one breast to improve their aim as archers, killed their male children and mated with men of other tribes when necessary.

Britain's Queen Boudicca, who ruled the Celtic Iceni tribe after the death of her husband around AD 50, was a fearsome leader whose towering height, wild red hair and knife-armed chariot horrified the occupying Roman troops.

Five hundred years later, the Arabian Queen Zenobia, who ruled the kingdom of Palmyra, led her troops to resounding victories against the Romans.

Women have also turned to terrorism and political violence.

In the French Revolution, they played a bloody role, and in the late 19th century, they were leaders of the violent People's Will organization in Russia.

Leila Khaled, a member of the Popular Front for the Liberation of Palestine, gained world prominence in 1970 when she helped to hijack an airplane, later plotting another hijacking after being jailed in Britain.

Germany's Baader-Meinhof gang was led by Ulrike Meinhof. And hundreds of women joined militant groups such as Peru's Shining Path, the Basque organization ETA and the Tamil Tigers — in which a female recruit trained to kill Indian prime minister Rajiv Gandhi, becoming the first woman suicide bomber.

Apart from terrorism, women have also committed violent domestic crimes in North America and Europe in recent years.

"Women commit the majority of child homicides in the U.S., more than 80 per cent of neonaticides; an equal or greater share of severe physical child abuse; an equal rate of spousal assault; about a quarter of child sexual molestations; and a large portion of elder abuse," says Pearson in her book.

Since the book was written in 1997, Pearson says, the trend to violence has continued.

"The issue is not that there are more violent women now, but that women are feeling more comfortable with being violent.

"The impulse to aggression isn't exclusively male, but women have been indirect in the way they are aggressive. Now, when the culture is more equal, it's more acceptable for women, too, to be openly violent," she says.

The recent trial of Kelly Ellard, accused of murdering 14-year-old Victoria girl Reena Virk, threw a spotlight on female gang violence, which appears to be increasing in Canada.

"Boys are raised to expect violence, and they learn what's done and not done," Pearson says. "Girls haven't learned any rules of engagement. They completely underestimate their own power. Group violence gives them permission, and they often go way overboard."

Although experts caution against predicting an "epidemic" of female violence, many are concerned that the trend is escalating, including in countries where the general level of violence is dropping. Violent women are an increasing part of popular culture in film and music.

As a result, a new debate has begun on the "true" roles of men and women in an age that deplores and glorifies violence.

"Until recently, most of the descriptions of (militant) women have been written by men," Davis-Kimball says.

"If female violence had been portrayed more accurately earlier, it wouldn't be so shocking today."

Additional articles by Olivia Ward