The insect flew into Van Gogh’s impasto of Olive Grove…
From The Art Newspaper:
The insect, of an unidentified species, flew into Van Gogh’s impasto of Olive Grove (Kröller-Müller Museum, Otterlo), in the foliage in the centre of the composition. It desperately tried to escape, weaving its way through the artist’s blue and green brushstrokes.
Astonishingly, the trail—which had not been noticed until the painting was thoroughly examined under a microscope—is 18cm long, equivalent to a quarter of the height of the painting. No trace of the unfortunate insect was found, so it is unclear whether it finally escaped or was buried in later overpaint when Van Gogh completed the composition.
Theoretically the insect could have been been trapped in the olive grove or the artist’s studio, but further evidence almost certainly means that the first phase of the painting was done outside. A fragment of a blade of grass (or plant stem), a probable seed and sand particles were also found embedded in Olive Grove. In another painting of the series, Olive Trees (Nelson-Atkins Museum of Art, Kansas City), the remains of a grasshopper were earlier discovered in the paint.