Ant 'midwives' help the birth of the blues – silver-studded, that is

One of Britain's prettiest butterflies is helped into the world by ants who act as "midwives" – guarding the freshly emerged insect while it inflates and dries its wings, new research has shown.

The remarkable story of the silver-studded blue and its ant-guarded emergence, pictured right, is told in the new edition of Britain's best-loved butterfly book – so sought-after that copies change hands for more than £100 – which is being republished next month, nearly 20 years after it first appeared.

The Butterflies of Britain and Ireland, by Jeremy Thomas and Richard Lewington, quickly sold out after its publication in 1991 and, because it was so popular but never reprinted, soon became valued at many times its original cover price of £16.99. Butterfly lovers scoured charity shops for copies but sometimes had to bid for it on eBay.

It was widely regarded as the best book about British lepidoptera ever produced, largely because the authors were the leaders in their fields. Jeremy Thomas, now the Professor of ecology at Oxford University, is acknowledged as Britain's top butterfly expert and his text is not only scientific but full of anecdotes about the butterflies and the people who collected them in the past. Richard Lewington is Britain's most celebrated painter of butterflies and moths and his exquisite, detailed illustrations are regarded as setting the standard by which other illustrators are judged.

The new edition of the book, which comes out next month, takes in the voluminous butterfly research which has appeared in the interim. It features two species wholly new to Britain – Real's wood white, and the geranium bronze – and many new discoveries, such as the account of the silver-studded blue and its ant midwives, shown here in Richard Lewington's illustration. The caterpillar depends for much of its life on black ants, spending the day, and finally pupating, inside ants' nests, where the ants care for it constantly – probably because the caterpillar gives off sugary substances which the ants consume.

'The Butterflies of Britain and Ireland' is being published by British Wildlife Publishing (, price £24.95, or £22 before 31 May.