I was on the Dart recently when a group of teenage schoolgirls boarded the train, chatting excitedly before sitting down beside me. Picking up the thread of their conversation, they began to fillet an absent schoolmate with deadly precision.
"She told me she was having laser treatment for her moustache," one girl said. This statement was met with a volley of "eews" from her eager-eyed friends. Their classmate was a loser, annoying and ugly, so a mutually agreed consensus was reached: she was a bitch and they weren't going to be her friend any more.
They reached their stop five minutes later and I watched them swing their schoolbags behind them as they got off, still talking and laughing. I thought of their absent schoolmate and found it all too easy to imagine her impending icy exclusion and the means of its spiky execution.
Why, I wondered, do little girls, made of sugar and spice and all things nice (or so the rhyme goes) turn into girls like these, who seemed to have about as much tact and kindness as a shoal of piranhas?
Is this sort of indirect aggression a common feature of the female teenage landscape? Or are these girls a bitchy exception to the general rule that girls are a fair sex?
Louise (61), a retired social worker, thinks not. "Teenage girls have always been catty," she says. "I still can't bear the smell of Imperial Leather soap because it reminds me of my girl's boarding school. If you didn't have this brand of soap, you were subjected to the most awful, sneering condescension, but girls could ostracise you for far less."
She continues: "There seemed to be so many things that could mark you out as a pity case, and the markers always seemed to change. By the time I'd got one thing right, they'd discovered another new benchmark for inclusion."
Louise says that leaving school was one of the happiest days of her life, "because I knew that, from then on, I could choose my friends. It felt so empowering. It still does".
The fact that a socially adept 61-year-old recalls the stomach-dropping sensation of exclusion so vividly is telling, and many other women have similar memories lodged deep in their adult psyche.
Sarah, an articulate, pretty 17-year-old, isn't surprised that memories of emotional bruises delivered long ago can arc across the years in this way. "It's because the memories are so painful," she says.
Sarah's bruises are fresher. She thinks that one of the most difficult aspects of female aggression is its covert nature. "I couldn't decide whether or not what was happening to me was bullying at first," she says, "or whether I'd just been dropped."
Well-integrated at school until the age of 14, she'd always had a group of close friends, Sarah explains how her problems started in Junior Cert year, when she returned to class after a week off school with flu.
"On my first day back, I thought my friends would be pleased to see me. I tried to talk to them and they were kind of off with me. I was confused, I suppose, and didn't know what was going on." Olivia describes the chilly moment when she realised that the sands had shifted. "I tried to catch my friends' eyes at lunch, but they carried on talking and looked at me as if they couldn't see me. Anyway, I sat down at a table next to them and they all stopped talking at the same time."
She continues: "Something as simple as this can send such a powerful message. I remember when it happened, I had this feeling of shame -- as if I'd done something so awful it meant I wasn't even worth speaking to but the thing was, I couldn't see what I could have done. I hadn't done anything."
A number of research studies on patterns of female bullying have found that this sort of hostile social manipulation is a classic example of the kind used by girls. The tools of social aggression typically include bitching about others, spreading rumours, breaking confidences and using code names to talk about classmates.
Other indirect harassments include prank calls, hiding personal property and 'dagger stares'. This 'old-school' type of bullying is largely confined to school premises and has been well documented by researchers across a broad range of study disciplines.
However, the nature of adolescent bullying has evolved due to the explosion of communication technologies. Girls have another weapon in their armoury with which they can harm schoolmates: the internet.
Teenage boys, who have traditionally tended to engage in more physical acts of aggression, also bully online. But while they initiate hostile online activity earlier than girls, research shows that teenage girls -- more frequent users of social networking sites -- appear to be both the primary targets and perpetrators of bullying in cyberspace.
Sarah says that this 'new school' kind of bullying is hardest of all. "I never knew when texts would come in or what I'd find on Facebook. Sometimes, I'd have managed to forget about school and then I'd get a text like, 'Sarah is so lame. She has no friends'.
"I might have just come out of the shower or be having dinner and it used to make me feel instantly depressed and anxious. The text would have been sent to loads of other people and it was so humiliating."
Though the cyber-bullying was sporadic, it became vitriolic and invasive; Sarah could receive up to 60 abusive texts in an evening and had postings on Facebook, such as "Ugly! Fat! Ugly and Fat!" Or, "I hate you. Everyone else hates you. Why don't you die?" She was also ignored online and had her password stolen. She'd find that hundreds of messages had been sent from her account to friends.
Like 85pc of teenage online bullying victims, Sarah didn't tell her parents because she was afraid they would "overreact" and cut off online access. "I felt embarrassed as well," she says, "and I didn't think there was anything they could do."
It seems that often, there isn't. The coercive approach to old-school bullying in schools has only been partially effective. Sarah says that when school administrators just get tough on the bullies themselves, it doesn't really work, but effective interventions into cyber-bullying are virtually non-existent.
A recent ruling in the UK determined that it's possible for an internet service provider to be liable for the content of sites which it hosts, but this doesn't help the here and now of an experience such as Sarah's.
I ask her why girls bully. "Girls go through a phase of it, especially between first and fourth years at secondary school. Everyone's trying to be in a clique; you need to be in a clique so you have each other ... but there's often a girl who's, like, the queen bee, really popular. She decides who's in and who's out, and the others are so anxious about staying in the clique that they go along with whatever she says."
Sarah also says that girls bully in groups online just for fun. "Facebook and mobiles make it so, so easy for girls to bully," she says. "You just click and send, there's no face to face." With more than a third of girls reporting direct involvement in bullying, technologies are clearly a powerful force for harm as well as good.
As for strategies, Sarah believes that things began to turn around when she finally confided in her mother. "I said I would tell her but only if she promised she wouldn't do anything about it. We just kind of broke it all down and went through it together and she helped me cope day by day, but I suffered the worst of it alone."
It seems to me that, as parents, we need to take a 'bull by horns' approach to informing ourselves about internet use.
But to facilitate frank debate about these issues with our daughters and promote genuine understanding we will need to adopt a different approach: less bull by horns, more delicate but absolutely clear-eyed. Perhaps then, teenage girls, made of sugar and spice and all things nice, might stand a better chance of staying that way.