London - If Twitter is the chirping chatterbox of the internet, trolls are its dark underground denizens.
The collision of the two is driving a debate in Britain about the scale of online hatred and the limits of internet free speech.
The furor erupted this week after several women went public about the sexually explicit and often luridly violent abuse they receive on Twitter from trolls — online bullies and provocateurs who send abusive or disruptive messages, often for their own amusement.
Many regard trolls as an annoyance to be ignored, but there are growing calls for action when their abuse crosses over into threats.
Police are investigating a threat of rape and murder made to Labour Party lawmaker Stella Creasy by a user with the Twitter name @killcreasynow. The crude and graphically violent tweet was one of many Creasy received after she tweeted in support of feminist campaigner Caroline Criado-Perez. Criado-Perez was sent a torrent of invective after she campaigned, successfully, for novelist Jane Austen to appear on a British banknote.
Two men have been arrested in connection with the Twitter threats, but have not been charged.
Claire Hardaker, a lecturer at Lancaster University in northwest England who researches aggression, deception and manipulation online, said that while the stereotypical image of a troll is of a man in his late teens or early 20s, they are a surprisingly disparate group — 30-something women and men in their 60s have been caught trolling.
Their motivation ranges from revenge to entertainment to boredom. While it seems a solitary activity, there is an online community of trolls who use sites like the anarchic forum 4Chan used to swap congratulations and criticism and egg one another on.
Twitter insists it takes the issue seriously and is planning to expand an abuse-reporting button, already available on its iPhone app, to other platforms.
"We absolutely do work with law enforcement on issues like these," Del Harvey, Twitter's senior director of trust and safety, told the BBC's "Newsnight" program. "These sorts of threats are against the rules. We suspend accounts when they're reported to us. We're working to make it easier to report those accounts. We think this is really important."