During their 1969 Hyde Park gig, The Rolling Stones released thousands of which insect?

The Stones in the Park generally refers to a free outdoor festival held in Hyde Park on 5 July 1969, headlined by The Rolling Stones and featuring Third Ear Band, King Crimson, Screw, Alexis Korner's New Church, Family and The Battered Ornaments, in front of a crowd estimated at between 250,000 and 500,000 fans.

It was the Stones' first public concert in over two years, and was planned as an introduction of new guitarist, Mick Taylor, though circumstances inevitably changed following the death of former member Brian Jones two days earlier. Fans started to arrive at the park with candles on 4 July in tribute to Jones, and by the morning of 5 July, 7,000 people had already gathered. Mick Jagger read a short eulogy on stage before the Stones' set began, reading two stanzas of Percy Bysshe Shelley's poem on John Keats's death, Adonaïs, from a calf-bound book. After this recital, several hundred cabbage white butterflies were released.

While the event is considered a memorable one by several critics, they also agree that it was not one of the Stones' best performances, and the guitars played during the concert were out of tune. In a 1971 interview with Rolling Stone magazine, Keith Richards evaluated their performance, "We played pretty bad until near the end, because we hadn't played for years ... Nobody minded, because they just wanted to hear us play again.