The London mayor has called on councils to "focus" on pest control after a fox is believed to have attacked twin nine-month-old girls in their home.
Lola and Isabella Koupparis were mauled on Saturday night as they slept in cots in an upstairs bedroom in Hackney.
In the attack, described as a "living nightmare" by their mother, Lola was bitten in the face and arm while Isabella suffered injuries to her arms.
Mr Johnson said "boroughs should focus on their duties for pest control".
Twins in hospital
The mayor said the councils need to "get together" and look at how they tackled pests.
"It's right that boroughs should focus on their duties for pest control because as romantic and cuddly as a fox is, it is also a pest," he said.
The twins remain in hospital in a serious but stable condition.
On Monday evening Isabella was transferred from the Royal London Hospital to Great Ormond Street Hospital (GOSH) for further treatment.
A GOSH NHS Trust spokeswoman said Isabella "continues to receive the highest possible levels of care from medical staff".
Lola remains in the Royal London Hospital in a serious but stable condition.
Their mother Pauline, told BBC London 94.9 that she and her husband Nick were watching television when she heard her "a funny cry" and went to check on the girls.
She described the "living nightmare" when she switched on the lights to see the girls covered in blood and the fox still there.
The twins' four-year-old brother who was also sleeping upstairs, was not hurt.
The fox is thought to have crept in through a door on the ground floor which had been left open because of the hot weather.
After the attack, pest controllers set fox traps in the back garden and one found in one of the devices on Monday night was humanely destroyed by a vet.