Castianeira is a genus of ant-like corinnid sac spiders first described by Eugen von Keyserling in 1879. They are found in Eurasia, Africa, and the Americas, but are absent from Australia. Twenty-six species are native to North America, and at least twice as many are native to Mexico and Central America.

The genus name Castianeira is treated as a proper noun in the original description, likely derived from the Greek mythological figure Kastianeira, who was described as the mother of Gorgythion in Homer’s Iliad. No explicit etymology was provided by Keyserling. This follows the convention of naming genera after classical names without reference to morphological characteristics.

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