Children wearing blue face paints have been ordered out of a zoo's monkey house after staff discovered they were scaring the animals.
Keepers of the small Geoffroy's marmosets at Twycross Zoo in Leicestershire were baffled when certain visitors made the monkeys sound warning calls and run up and down their branches.
As an experiment, one of the zoo's management volunteered to have her face painted blue and was shrieked and stared at by the monkeys as she walked through the tropical exhibit.
Human resources manager Barbara Chawner said she was glad the mystery of the marmosets' strange behaviour had been solved.
She said: "On occasions I have had a red face, but I have never been blue before.
"When I heard of the strange behaviour of the marmosets I was concerned and volunteered to have my face painted in the interest of public safety."
Keepers said the marmosets would not attack anyone, but have banned blue faces from the tropical house to avoid causing the animals stress.
A zoo spokeswoman said the attraction's face painter now has to warn children who want the blue tiger design that they must visit the monkeys before having their faces painted.
She said experts could not explain why blue face paint in particular was scaring the small squirrel-like monkeys.
