Museum curators have made a surprise discovery in Vincent Van Gogh's Olive Trees: a grasshopper embedded in the paint.

The experts from the Nelson-Atkins Museum of Art in Kansas City discovered the insect - missing its abdomen and thorax - 128 years after it was painted.

Van Gogh was a famous proponent of plein air painting - the practice of painting outdoors - and it is thought the grasshopper unintentionally became part of the canvas while the artist was at work outside.

"Van Gogh worked outside in the elements," Julián Zugazagoitia, the Nelson-Atkins Museum of Art director, told the Kansas City Star. "And we know that he … dealt with wind and dust, grass and trees, flies and grasshoppers."

The grasshopper was spotted by the curators during a cataloging project. It is camouflaged in the brown and green colours in the foreground of the painting.