What was the first animal to fly in an airplane?

John Moore-Brabazon, 1st Baron Brabazon of Tara (1884-1964) an English pilot and politician, took a pig named Icarus II onboard for a flight as a joke, and witty way to "prove" that pigs can fly in 1909.

Moore-Brabazon first flew solo in November 1908 in France in a Voisin biplane. He later became the first resident Englishman to make an officially recognized aeroplane flight in England on 2 May 1909, at Shellbeach on the Isle of Sheppey.

On October 30, 1909, flying the Short Biplane No. 2, he flew a circular mile and won a 1,000 pound prize offered by the Daily Mail newspaper. Just a few days later, on November 4th of the same year, as a joke to prove that “pigs could fly”, he put a small pig in a waste-paper basket tied to a wing-strut of his plane. (This may also have been the first live cargo flight.)

Fortunately for the pig, it was smart enough not to attempt skydiving.