The trails left by dust devils on the Martian surface can be up to several hundred metres wide and several kilometres long. They tend to form in the afternoon on warm spring and summer days, when the surface is illuminated by sunlight for a longer time, and thus heats up more. Nevertheless, dust devils have also been observed during the winter months. Dust devil tracks may run straight or follow curved or winding paths, as well as intersecting or overlapping with one another. Their lifespan is relatively short, as they tend to be covered over again by light-coloured sand that is whipped up by dust storms, so that they disappear within a matter of days or months.