The UK Butterfly Monitoring Scheme (UKBMS) said a record-breaking hot summer for the UK in 2018 meant a jump in numbers of two-thirds of UK butterfly species.
Consistently high-temperatures from April until July meant 39 out of 57 species saw increased numbers compared with 2017.
UKBMS also announced in April that two of the UK's rarest species were recorded in their highest numbers since records began in 1976. These were the endangered Black Hairstreak whose numbers rose by more than 900% and the threatened Large Blue which rose by 58%.
London Wildlife Trust director of conservation, Mathew Frith, told Reuters: "We had a very hot summer, long dry periods, that was particularly good for a range of butterflies and that's something which is in some ways testimony to the conservation work of a whole range of organizations."
However, it was not all good news. UKBMS data has showed around two thirds of species (36 of 57) have shown an overall decline since 1976 with 21 species showing long-term decline.
UKBMS data is gathered by thousands of volunteers throughout the summer.
2873 sites were monitored in 2018.
