In ancient myth, Achilles and Patroclus were two Greek heroes of the Trojan war whose intense bond was believed by some to have turned into a sexual relationship.

In modern science, they are a bull, Achille, and a donkey, Patroclo, whose tender interspecies affair has helped to shed new light on social and sexual interactions between animals.

Researchers say the two males have been spotted licking and rubbing each other, with the bull sometimes mounting the donkey.

The team said while other donkeys attempted to avoid Achille’s attentions and showed threatening facial expressions towards him, Patroclo often presented his hindquarters to Achille and nibbled him.

“It is really, really unusual,” said Dr Elisabetta Palagi of the University of Pisa in Italy, who co-authored the study. “And it is the first time it is reported in literature.”

Achille with Patroclo.…