Five monkeys have been found on board a container ship heading for Rotterdam port, primate charity Stichting Aap said on Wednesday.

The five primates, said to be wild crab-eating macaques, were caught by the crew and will be handed over to the foundation when the Maersk freighter arrives in the Dutch port city on Wednesday.

The primates are thought to have climbed aboard the ship in Malaysia. It is not yet clear if they will be returned, news agency ANP reports.

‘In practical terms, they could be sent back but it will be decided later whether to do this or send them to a zoo,’ a spokeswoman for the foundation said. ‘They will first be given a health check.’

Crate

The monkeys were first running wild on the ship but were eventually all caught and put in a crate. ‘It is not a big crate but you have to do the best with what you have,’ a spokesman for Maersk told ANP.

The crab-eating macaque is regarded as one of the world’s 100 most invasive alien species because it is so adaptable and a generalist feeder. The males can reach up to 55 cm in length.