Adriana Orme and Holly Le Gresley admitted earlier this year to being part of the network
The judge describes the women's behaviour as depraved, sickening, wicked
He added some of the videos depicted "extreme sadistic violence"
Members across the world paid for baby monkeys in Indonesia and other Asian countries to be tortured, and killed, for pleasure
The group began life on YouTube, before moving to messaging app Telegram
It was exposed after BBC Eye journalists went undercover on Telegram
Prosecutors paid tribute to the work of charity Action for Primates
Warning: This report contains upsetting and disturbing content
The judge has now been speaking about Le Gresley's apparent enjoyment of the injuries being caused.
He said her online nickname, The Immolator, "indicated a desire to maim or torture".
"You seemed to revel in that name", he said.
Referring back to the online conversations about the legal risks of what they were doing, the judge recalled how Le Gresley was keen to avoid having her name in the papers.
He noted "a full press bench" in the courtroom today.
The judge has continued: "I find myself still in a state of disbelief."
He said Le Gresley and Orme's actions were "beyond comprehension for most of society", adding "why there is such a forum is beyond comprehension for most decent people."
He told the pair: "You promoted the physical torture of monkeys by others, you shared videos and images of such torture and abuse, retained images and videos for what appeared to be your own pleasure and amusement."
And he told Le Gresley she had "caused significant pain, torture and death to the monkeys in Indonesia".
The judge told the women that they both in the comfort of their own home engaged in chat rooms on the internet.
He said: "Perhaps in that environment you took leave of your senses and a real recognition of reality as apparently some people appear to do when engaging with others on the internet."
The judge told both women their offences represented a course of conduct that can only be described as "depraved, sickening and wicked".
He said: "Neither of you can explain away your conduct as pure fantasy as you seemed to assert in interviews with police."
Orme's defence lawyer has concluded his mitigation and His Honour Judge James Burbidge KC has begun his remarks.
The court heard Orme had good prospects of rehabilitation.
Mr Myrie said there was very clearly a pathway that had been suggested by all the professionals who have assessed her.
Orme has been described as a woman with no previous convictions and of good character.
The court has heard she is a "a loving mother and grandmother", who is also caring for her own pet and "caring very well".
Her lawyer went on to add that she pleaded guilty and "in essence accepted what she did".
The court also heard she had taken steps to address her behaviour and was on the waiting list for cognitive behavioural therapy.
Orme's barrister has tried to describe his client as a woman with "a considerable mental disorder which focuses in on inappropriate activities".
But the judge replied: "That jump I find difficult. She had the same mental condition from start to finish.
"She starts by wanting to stop this outrageous behaviour and then commits such outrageous behaviour herself."
"She'd got a taste for it," he said.
Orme is rocking in the dock as the court hears discussions about her her life and behaviour.
The court has heard claims she is socially awkward, isolated and alone.
However, the judge has said she has a loving family, exercises her dog and is sociable with neighbours.
Orme, sitting in the dock, has her hands on either side of her face.
The court has been told Orme has several physical illnesses and injuries including chronic pain and fibromyalgia.
Defence barrister Curtis Myrie said she has not been able to work since being in the UK and has been housebound and is left alone by herself for long times.
However, the judge has questioned this, referring to other references about how she walks her dog.
The judge said: "She doesn't sound like she's housebound."
Orme's barrister has been telling the court she came to the UK from the Netherlands in 2014.
She remarried here, Mr Myrie said, and her character references he said, had been "very positive".
Curtis Myrie is defending Adriana Orme and about to speak in mitigation.
Speaking further about Le Gresley's conditions, Mr Walkling said she has been affected by anti-depressants and suggested this "could affect her levels of empathy".
"She isn't a risk or danger to the public in our submission," he said, adding that she has no previous convictions.
But he told the court: "She will find custody extremely difficult due to her conditions."
Le Gresley "has a long history of depression and anxiety and is likely to be diagnosed with autism disorder", the court was told.
The court heard Le Gresley had found the two years since her arrest very difficult.
She had been having to live with the knowledge of how she had behaved, her defence counsel said, in mitigation.
Le Gresley's defence barrister Tom Walkling has said: "I hope to persuade the judge to give a suspended sentence.
He described her as a woman of previous good character who was "extremely remorseful".
The court heard she pleaded guilty at the first opportunity.
Mr Walkling said: "She has significant problems with her physical health, in particular, chronic fatigue syndrome."
He added that she had been diagnosed with at least one, possibly two, mental health problems.
Moment BBC reporter returns tortured monkey into wild
As the prosecution concludes, here is the moment a rescued monkey was returned to the wild.
Mini had two years of rehabilitation at a sanctuary run by the Jakarta Animal Aid Network.
See her video here.
The maximum sentence for both defendants is five years, prosecutor Ben Close has told the court.
Le Gresley's searches included how to delete and share material and how to hide her Telegram usage.
One search term was: "The urge to torture animals, should I see a doctor?"
The court heard she also researched where she could buy a monkey in the UK.