Theridion viridanum is a species of Theridiidae that is endemic to New Zealand.
This species was described in 1887 by Arthur Urquhart from female specimens.
The female is recorded at 3mm in length.
This species is only known from Waiwera, New Zealand.
Under the New Zealand Threat Classification System, this species is listed as "Data Deficient" with the qualifiers of "Data Poor: Size", "Data Poor: Trend" and "One Location".