Fifty Years On, The 1975 Emperor Season

  Fifty years ago, Emperoring was very different. The Purple Emperor was considered a rare butterfly, confined to a few southern oakwoods. People wanted to catch pristine males, and pin them; or net gravid females, for breeding (and subsequent pinning and/or releasing). Nobody photographed butterflies then, at least not in the wild – the technology wasn’t there. No one counted butterflies; few studied their ecology, or even kept diaries. 

  An article by Alison Ross in The Times (Aug 23^rd 1975) describes how ‘teams of nature conservationists patrolled the woods known to collectors … and also talked to Forestry Commission officials … to explain the need for the preservation of sallows.’ This drama centred on Bernwood Forest on the Bucks-Oxon border but was replicated elsewhere, particularly in Alice Holt Forest, Hants, and Chiddingfold Forest, Surrey-Sussex. The real threat, of course, was the felling of sallows, which was standard forestry practice.

  This was a truly great butterfly year, which prepared the way for the Long hot Summer of 1976. But the roots of 1976’s greatness lie deeper: the summer of 1974 had been good, and saw butterfly populations rise; they rose further in 1975, so that 1976 was the third good butterfly year on the trot.

  The winter of ‘74-75 was mild. It was followed by a cool, late spring with snowfalls down south in late March and early April, a severe late frost at the end of May, and a snowfall in the London area on June 2^nd (Snow Stopped Play in Derby v Lancs at Buxton that day). 

  The great summer of 1975 then began in earnest: ‘Change in the weather, is so extreme’, so croaked Bob Dylan in the album of the summer, Blood on the Tracks. May and June were warm and sunny.  

  The White-letter Hairstreak stormed Butterfly of the Year, a considerable achievement as 1975 was one of the best Purple Emperor years on record, but White-letters were everywhere. Alison Ross describes how they ‘fluttered over the dying wych elms in profusion.’ My diary for July 10^th recalls the antics of some 50 White-letters active over a nondescript patch of English Elms in a roadside scrub thicket – but any elms revealed similar profusions. Sadly, Dutch Elm Disease became rampant that summer. 

  Despite the cold, late spring, the Purple Emperor season began at the start of July. I saw my first in Straits Inclosure, Alice Holt Forest, on July 5^th; then saw at least half a dozen fresh males in Southwater Woods (north of Knepp) on the following day (having seen none there on July 1^st). This is an early start date for that era, and is remarkable as it happened after such a late spring. 

  Clearly, the insect had romped through the 4^th and 5^th larval instars, and the pupation / pupal period, during a fine May and a very good June – and it needs to romp through the vulnerable pupation & pupal period if adult numbers are to be high.

  The 1975 Purple Emperor season started and ended in hot weather, but the bulk of the flight season was dominated by weak areas of low pressure, which brought spells of cloud, patchy (light) rain and drizzle, and Moderate or even Fresh south-westerly winds. 

  But Emperors erupted whenever the sun came out. Crucially, many male territories held more than one occupant, which meant they were fully active – sparring against each other. I was seeing 12-15 apparent individuals a day, most of them on leeward, east-facing wood edges. Many of my sightings were of sparring pairs, not singletons. 

  On July 26^th a big anticyclone developed, and on that very day the Long Hot Summer of 1976 was born. Emperor males quickly burnt out in the heat, leaving a few worn females to stagger into early August. I saw my last of the year on August 2^nd, a female. Then they were gone. What do you do when the party’s over? 

The weather got better and better, hotter and drier, leading into a quintessential autumn that brought a strong third brood of the Wall Brown, and Pink Floyd's classic album Wish You Were Here.