Large swaths of vineyards on the slopes of Sicily's volcano Mount Etna also remain free of the phylloxera louse. Some vines are more than one-hundred-fifty years old, predating the phylloxera infestation in Sicily (1879–1880). Part of the reason for this is the high concentration of silica sand and very low (less than 3%) concentration of clay in the volcanic soils. In this environment (> 400m AMSL), the surface water from heavy bouts of rain seals the soil so perfectly that it imprisons the louse, effectively drowning them before they are able to thrive.