The pine wood nematode is related to the roundworms which parasitize humans. Once, they only lived in the soil and had a very limited range, but at some time or other they evolved a symbiotic relationship with pine sawyer beetles (long-horned beetles of the genus Monochamus in the Cerambycidae family; their larvae are called sawyers because of the noise they make while feeding in a log or stem).
線蟲與寄宿人身上的蛔蟲同類，但線蟲原本只在土壤中游動，活動範圍有限，攻擊松樹的松材線蟲卻與天牛完成高度「演化」，躲在天牛呼吸氣孔。