Mangua caswell is a species of Physoglenidae spider endemic to New Zealand.

[1] This species was described in 1990 by Ray Forster from male and female specimens.

[1] The holotype is stored in Te Papa Museum under registration number AS.000108.

[2] The male is recorded at 3.49mm in length whereas the female is 3.61mm.

[1] Under the New Zealand Threat Classification System, this species is listed as "Data Deficient" with the qualifiers of "Data Poor: Size" and "Data Poor: Trend".