蛲虫（学名：Enterobius vermicularis，英文Pinworm），别名:针状虫、坐虫，线虫动物门中的一类肠道寄生虫，是蛲虫病的病因。在全世界均有其分布。

成虫虫体外型有如粉红色线头，前端有三片唇，且角皮层衍生成肥厚的头翼，有明显的葫芦状食道与球状澎起的食道球。

雌虫体长8~13x0.3~0.5毫米，尾端呈明显针尖状，在显微镜下可见其阴门开口位于体表前三分之一的腹面处。雄虫体长较雌虫小，2~5x0.1~0.2毫米，尾部卷曲。在显微镜下可见一部明显之交尾刺。

虫卵为米粒状不对称形，大小为50~60x20~30微米，虫卵呈大写字母“D”形，卵壳厚、没有卵盖，透明虫卵，虫卵发育很快，内容物常见为U字形幼虫。

The pinworm (species Enterobius vermicularis), also known as threadworm (in the United Kingdom and Australasia) or seatworm, is a parasitic worm. It is a nematode (roundworm) and a common intestinal parasite or helminth, especially in humans. The medical condition associated with pinworm infestation is known as enterobiasis (a type of helminthiasis) or less precisely as oxyuriasis in reference to the family Oxyuridae.