Trump's father has doubled down on his pledge to build a wall on the border with Mexico, leading to a partial shutdown of the US government. The president himself has described some migrants in similar terms, saying in May last year that: "You wouldn't believe how bad these people are, these aren't people, these are animals."
The Instagram post by Trump Jr - who has previously drawn fire for comparing Syrian refugees to a bowl of potentially deadly Skittles candy - drew criticism on social media. "This is racism on steroids," one user wrote on Twitter, while another tweeted: "The only zoo animal is Junior himself."