Norway’s "most famous chimp", Julius, who resides at the Dyreparken Zoo in Kristiansand, fell seriously ill after a visitor chucked a plastic bottle containing an unknown drug into his enclosure. During his drug-induced state, the chimp inflicted some severe injuries on himself, including gnawing on his own arm.

The event happened last month, and the 39-year-old chimp is recovering from the incident, a recent announcement from Dyreparken Zoo and Amusement Park said. Meanwhile, the zoo is using CCTV footage of visitors and working with the police to try and find the culprit.

"We are shocked,” Rolf-Arne Ølberg, a vet at the zoo, said in the statement. “We're so glad he's getting better, and his wound is healing. It could have been much worse."

On the evening of February 21, staff became concerned after noticing Julius was behaving abnormally. Zookeepers put him under anesthesia to check him over after noticing he was sitting alone in an agitated state with nasty wounds along his arm.

The team was initially stumped, thinking perhaps the arm was infected, making him act strangely, but it was later reported that guests at the zoo saw somebody throw a bottle into the enclosure.

“It was only then we started to suspect that he could have acquired something that could explain the abnormal behavior,” says Ølberg.

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Vets took blood and urine samples at St Olav's Hospital in Trondheim, which confirmed he had ingested notable quantities of an unspecified drug. Out of the eight chimps in the herd at Dyreparken Zoo, Julius – who has a love of fizzy soda – is the only one capable of unscrewing bottle caps, so he was the only individual who fell prey to the malicious prank.

“Over the following days, our main focus was to take care of Julius,” Ølberg said.”We are first and foremost grateful and happy that it seems to be going well with him. The wound now heals and Julius behaves normally.”

Julius was born at the zoo in December 1979. As a young chimp, he was abandoned by his mother and ended up being adopted by zoo director Edvard Moseid and his family. He’s well-known in Norway because he was featured in a kids' documentary on the Norwegian Broadcasting Corporation in 1981, according to Norwegian newspaper Dagbladet, and for multiple successful escapes from his enclosure.

A recent genetic analysis showed that he belongs to a subspecies of the common chimpanzee, known as the West African chimpanzee or western chimpanzee, found in Côte d'Ivoire and Guinea. According to the zoo, conservationists have been looking at Julius to help with breeding programs for the western chimpanzee, which are critically-endangered with extinction.