Nigma is a genus of cribellate araneomorph spiders in the family Dictynidae, and was first described by Pekka T. Lehtinen in 1967. They have a wide distribution, including Eurasia, North America, and Northern Africa. N. walckenaeri is one of the biggest members of the Dictynidae, growing up to 5 mm long. They are translucent green and sometimes have red or black markings on the abdomen.