The Avro 531 Spider was a prototype First World War British sesquiplane fighter aircraft built by Avro.

In tests, the aircraft demonstrated exceptional performance, handling, and pilot visibility however the time it flew, the War Office had already selected the Sopwith Snipe for mass production.

This had standard interplane struts and was intended as a racing aircraft.

It was never used for this purpose, however, because it was discovered that it had a faulty wing spar, so the Avro firm used it as a hack instead from May 1919 to September 1920.

[1] Data from Avro Aircraft since 1908 [2]General characteristics Performance Armament 1 × fixed, forward-firing .303 in (7.7 mm) Vickers machine gun