A bizarre video has emerged from the US of two leopard slugs mating on a tree.

The footage, captured in a backyard in Columbia, Maryland on August 16, shows the slugs twisting their bodies around one another.

The molluscs then extend their long, blue penises and entwine them to complete the mating process.

Terrestrial slugs are hermaphrodites – so by wrapping their penises around one another, leopard slugs fertilise each other’s eggs.