By Patrick Barkham

Butterflies are full of surprises and this year they have saved their biggest until last: in the midst of an awful November, subtropical butterflies have been spotted on England’s south coast. The remarkable appearance of the long-tailed blue, a butterfly happiest in the heat of Africa or Australia, raises a mystery: will these insects simply die this winter?

Until recently, the long-tailed blue, or Lampides boeticus, very occasionally arrived in hot summers: notably in 1945, and 1990 when it pitched up in Gillespie Park, north London. In 2013, however, there was an unprecedented invasion. Summer arrivals laid eggs on everlasting peas (ironically a garden plant gone wild, imported from Italy) and in October offspring emerged: 109 were counted. This year it’s happened again. But the emergence of a British born generation has been delayed by the gloomy autumn. If it stays mild and the rain stops, more could yet hatch.