马陆（学名：Diplopoda，英文：Millipede），又称千足虫、千脚虫，倍足纲节肢动物，陆生。大多数马陆的活动速度都比蜈蚣慢。身体有多节，头部有触角，头四节为头胸部，余下皆为腹部。生活在潮湿地方，大多以枯枝落叶为食。有时会啃食植物幼苗，因此可能会被认为是害虫。现时本纲已描述的物种有约8000种，但估计只占地球上所有倍足纲物种的十分之一。

除第一节及最后一节外，每一体节有两对脚，一般物种大约有从36只到400只脚。当中比较较特别的有Illacme plenipes和Sibiriulus baigazanensis。在俄罗斯研究员米洛斯拉夫·萨赫涅维奇于西伯利亚的阿尔泰生物保护区首次发现Sibiriulus baigazanensis之前，Illacme plenipes是当时世界上腿最多的生物。Sibiriulus baigazanensis的身长几公分到20公分不等，其中最多拥有超过700支脚。相反的，Pill millipedes却很短小，而且遇袭击时可假死片刻，把自己蜷缩起来成为球状。马陆味臭，令鸟兽都不爱吃。马陆体内有一种药物，可以发挥驱蚊作用。

Millipedes are arthropods in the class Diplopoda, which is characterised by having two pairs of jointed legs on most body segments. Each double-legged segment is a result of two single segments fused together as one. Most millipedes have very elongated cylindrical or flattened bodies with more than 20 segments, while pill millipedes are shorter and can roll into a ball. Although the name "millipede" derives from the Latin for "thousand feet", no known species has 1,000; the record of 750 legs belongs to Illacme plenipes. There are approximately 12,000 named species classified into sixteen orders and around 140 families, making Diplopoda the largest class of myriapods, an arthropod group which also includes centipedes and other multi-legged creatures.