Caught by the River

His Imperial Majesty

Sue Brooks | 15th August 2020

Resident Lepidoptera-lover Sue Brooks reviews Matthew Oates’s natural history of the Purple Emperor butterfly.

At the end of his previous book In Pursuit of Butterflies, Matthew Oates celebrates his 60th birthday on August 7th 2013 with a late season encounter with a female Purple Emperor in one of his favourite places — Marlpost Woods. He is in a philosophical mood – for 50 years I have just been scraping the surface, dabbling at the shallow end. It is time to venture deeper. He floats the idea of concentrating on a single butterfly, the one that matters most — His Imperial Majesty, the Purple Emperor, Apatura iris — and embodies it with a pen and ink drawing of a young boy in an english landscape holding a butterfly net. 

Dabbling at the shallow end does not do justice to a memoir that has been a guide and inspiration to countless beginners like me, but I remember thinking a whole book about a single species would probably be a slim volume. I was completely wrong. His Imperial Majesty is 390 pages, including the excellent Appendix, and riveting from start to finish.   

No natural history of a creature of such dazzling beauty could omit the terrible slaughter inflicted by the Victorian naturalists who pursued and killed the Purple Emperor in monstrous numbers for their collections. Oates shares their passionate intensity but never the desire to kill or possess. His mission has always been to understand and pass on the knowledge he acquires. To that end he has kept copious and detailed diaries for six decades, especially of the seasons when the Purple Emperor is on the wing, i.e. from mid June to the end of July/beginning of August. The problem with this particular butterfly has been, until the population on the Knepp Estate in West Sussex began to soar, that the Purple Emperor spends most of its time in the canopy of tall trees.

Rewilding at Knepp has taken the Purple Emperor story into another dimension. Without it, this book would not have been written. The humble and much-maligned Sallow or Goat Willow, Salix caprea, spread widely in the last 20 years over flat arable fields with well established oak hedges — a perfect habitat for studying the behaviour of the adult Purple Emperor in the presence of the vital larval food plant. It enabled Oates to build up a body of evidence which challenges many of the previous beliefs about the butterfly — essentially that it is not just a forest species found in a few sites in Southern England. Instead, it is highly mobile, opportunistic and adventurous, and could be seen wherever the favoured Sallow grows — in sheltered woodland edges, in parks, and even gardens with tall trees not far away. 

The chapters detailing the hard-won investigation of the best kind of Sallow leaves to provide food and shelter for the various stages (Instars) of the larvae are, for me, deeply moving. This is winter work, far away from sunny afternoons on a Knepp safari watching sex-driven males battling with rivals. This is patient searching for where the female Purple Emperor may, so carefully, have laid her precious egg — a private moment rarely seen by human eyes — followed by solitary expeditions for the rest of the year trying to keep track of the larvae as they slowly progress through the Instars. Oates tentatively concludes that the highly vulnerable 1st Instar needs medium-sized leaves which are matt green and soft in texture, growing on 1st year twigs of young Sallows. Such dedication and diligence can only be described as a labour of love. He really cares about these tiny creatures and it comes as no surprise to read that when he was following the hibernating stage and over half the larvae studied disappeared, he had to space out his visits from fortnightly to monthly because the losses became unbearable. 

The story reaches a climax with the glorious summer of 2018 — a record-breaking year for His Imperial Majesty when more than 300 were seen at Knepp on Midsummer’s Day. In Matthew Oates’s words, it was the most profound temporal experience of my life, providing invaluable data on the behaviour of the adult in such large numbers and evidence of successful development to the second Instar of the larvae.

At times, for anyone who has yet to be seduced by this exotic, tantalising creature, the behaviour of the disciples is almost as fascinating as the butterfly itself. Serious Emperorphiles follow Oates’s Purple Emperor blog and regard themselves as loyal servants. It is a matter of unrequited love and lifelong fidelity. Interestingly it is the male butterfly that carries the power for mostly male admirers: the female is described as shy and retiring, decidedly aloof and exceptionally hard to study. She seems to spend most of her time trying to avoid the attentions of alpha males, which often pursue her in furious groups. 

July 17th 2019 was my first and only encounter with a Purple Emperor. Knowing its reputation at Knepp, but not knowing where to look, I found myself at the end of the afternoon in the presence of what was unmistakeably a Purple Emperor fairly low down in an oak tree. I have a blurred photo to prove it and best of all, I was alone. The heartfelt pleasure of that moment stays with me and does feel like a kind of initiation. I know now that it was probably a female and that is an extra source of pleaure. I doubt I could enjoy watching some of the more extreme bullying inflicted by the males that Matthew Oates describes. On the other hand, I investigated the twenty-foot Goat Willow in my garden and took samples of the leaves. They match the pictures in Chapter 9 exactly, even to the slightly curved tip, and for a few delightful minutes I imagined a Purple Emperor life cycle outside my back door. 

Everything about this book is uplifting. It is packed with information about where and when to search for Apatura iris, it is optimistic for the future and above all it is written by a superb naturalist who exudes enthusiasm and happiness. The little boy with the butterfly net has taken Thoreau’s advice:

Go confidently in the direction of your dreams. Live the life you imagined.


His Imperial Majesty: A Natural History of the Purple Emperor is out now, published by Bloomsbury, and is available from your local independent bookshop, priced £20.00.