Didymus metrosideri is an endemic weevil from the Kermadec Islands in New Zealand.

[2] This species was discovered by W. L. Wallace during the 1908 Kermedec Islands expedition.

D. metrosideri was originally described by Thomas Broun as Acalles metrosiderae.

[3] In 1982 G. Kuschel proposed that the new genus Didymus replace the original genus Acalles.

[2] Specimens of this beetle have been discovered on Raoul Island and on Macauley Island.