The Future of the Purple Emperor in Hampshire &

Isle of Wight

 

 

A spectacular butterfly, and for those who have seen it will know it leaves a lasting impression. It is hard to predict where and when this species might turn up, as it has had so many see-saw seasons in the county. There are the obvious places where it’s almost guaranteed to be seen, but there are other sites now where twenty years ago they were seen in ones or twos, but now seem to have almost disappeared. The reason is the weather has a big impact on most species, but it seems to have larger impact on this species being arboreal, and bad weather can have a very adverse effect on its numbers from one season to the next.

 

The damp conditions in winter play a big part and also in autumn mildew can affect the sallow, which is the foodplant for the caterpillar, as the leaves tend to go yellow and shrivel up leaving the females with less target areas on which to lay her eggs. With the prospect of a warm early spring the other ‘enemy’ can be the Blue Tit, which forages in the Oak canopy looking for suitable caterpillars to feed their young and the Emperor tends to get the brunt of the feeding frenzy.

 

In the summer around the date of St Swithun’s in July, gales tend to do damage to the egg-laying females and also when they are mating or hatching depending on the time of the season. This tends to make the mating season poor, which then leads to a poor egg-lay, which seems to have been the norm over the last couple of seasons.

 

Another problem seems to be sallow felling in woodland where suitable oak plantations are ‘ripe’ for harvesting, and large ride side sallow are taken out to harvest the Oak or other trees. Sallow tends to take its time in recovering, although it is a fast growing tree. Purple Emperors can tolerate disturbance if there is sufficient sallow and areas of mature trees for them to mate and use for assembly points, but too much disturbance and they tend to become more secretive and harder to find. Some woods such as Whiteley Pastures are now surrounded by housing so I now have to go deeper into the wood to find it.

 

Despite weather, sallow destruction, and human disturbance, the Purple Emperor in Hampshire is still extant in most of the larger woods in the county. The obvious gap is the New Forest where this species could be seen in Sallow rich enclosures up to the second world war. Conifer plantations replaced a lot of the timber used for the war effort, but the forest is now being replanted with natural species, and the sallow plantations are slowly coming back.

The last records from the New Forest were in 2012 from Hale Purlieu (SU200180) and Costicles Inclosure in 2008 (SU326106 but there have been other records from the fringes of the forest like Southampton Common and Rownhams Wood. I have identified several sites within the wood worthy of investigation, these being Hursthill Inclosure, Busketts Lawn Inclosure, which is next to Costicles Inclosure, and Matthew Oates has identified several areas around Pondhead Inclosure and the roadside verges along from Lyndhurst the A337, where there are good areas of sallow worth investigating.

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A wood that has had good average sightings over the last twenty years is Alice Holt Forest, the area known as Abbotts Wood Inclosure is the woods mainstay where in a good year I’ve seen up to (25) males patrolling the Oak canopy and Assembly Points dotted around the site. Nearby Straits Inclosure having been on a downward trend over the last few years.

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In West Wood and Crab Wood near Winchester I normally see up to a dozen males yearly, and strangely enough the city of Winchester seems to harbour a colony of the species. Witnesses saw a female at a hat fair in the grounds of the Cathedral in 2015, and several years ago a female came down where a mother was changing her baby’s nappy in the main park in Winchester. Another held up the traffic on the main road, where a recorder witnessed one flying across the road and stopped his car. In 2020 several females were seen in the city, one escaping the clutches of a cat, this paints the city as one of the purplest in the south of England as these butterflies are annually reported from this area. 

 

Other towns of note are Basingstoke where there is an excellent wood known as Carpenters Down Wood, here the Purple Emperor is seen regularly, although this has been threatened by new house building. Also another wood where I’ve seen the Emperor  but is well under recorded is Butterwood, alongside the M3 Motorway. This is where I cut the ‘mustard’, as it were, as it is situated close to Reading which was my home town many years ago. There are occasional records from Hook and the Camberley areas, Bartley Heath and Odiham, plus  the Basingstoke Canal, which winds its way around north Hampshire. There are some excellent mature Oak trees beside the canal, with many good sallow stands along its banks. However despite all these micro-woodlands dotted around the area the species is under-recorded. 

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In the far north of the county records can be very scarce, but one area known as Herbert Plantation had regular records up to a few years ago, and an assembly point had been discovered on site. The species has also been discovered close to the Hants/Berks border at Newbury Common. On the airfield sallow stands soon grew on the old abandoned runways, thus showing the Purple Emperors adaptability to moving into areas which can sustain a small viable population, and able to utilize smaller woods if conditions are right.

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Another area under recorded is Pamber Forest, which is another site I used to frequent but is only noted on transect now, although truth be known it’s probably more common there than records show. The Purple Emperor is also under recorded in the Overton area, where there are many satellite woods dotted around the arable farms.

 

Part of the Forest of Bere known as Havant Thicket is where I’ve been concentrating a lot of my efforts lately as its only 20 minutes down the road from where I live. It’s used by dog-walkers and is on the fringes of a major motorway, housing, and in the future a large Reservoir, which will be built in the middle of the wood. How this will affect the butterfly nobody really knows. Havant Thicket is criss-crossed by many good rides with good sallow content and several years ago on a field trip we saw several males playing-tag around small oaks in the main ride, just behind the main car-park. There is also a good Assembly point utilised by several males every year, which is well worth looking at.  

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Closer to Portsmouth, Creech Wood just to the north of Portsdown Hill has a small viable population with excellent sallow stands in the wayleaves, the area underneath the electricity pylons. Here the Purple Emperor breeds, and I’ve witnessed females laying on the sallow many times in the past, and 2020 was no exception. Over the last few years there has been some interesting sightings within the boundaries of Portsmouth. A female was seen on top of a 'wheelie bin' in Paulsgrove. Also a male was seen in the shopping centre known as Gunwharf Quays. This is a most 'bizarre' sighting, but the recorder has been on my field trips, so there is no evidence of a mis-identification. This could have been a male trapped in somebody's car, and managed to get out when it was parked up. I shouldn't be surprised though if the Purple Emperor gets to Portsmouth naturally, if it isn't already here... as there is a 'sallow' corridor along the A3 motorway from the Havant Thicket area.  Sightings from the Hilsea Lines area should be the norm in the future.

 

There are other potential "Purple Emperor" woodlands to look at close to Marwell Zoo, Matthew Oates mentioned this site when he was looking for it's caterpillar which he eventually found on sallow next to the leopard inclosure! I’ve visited the woods right next door to Marwell Zoo, known as Leybushes Copse and Sladford Copse, where I have been told the adult Purple Emperor used to be released.

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Other sites worth mentioning where records have petered out over the last few years are Weston Common and Lasham Wood. Matthew Oates used to visit these two sites in the late 70’s and early 80's, which were then probably some of the best sites in southern  England.

 

I've looked at other woods in and around the Alice Holt Forest Complex to the west of Alice Holt and Hartley Wood look to have very good potential. Also Selbourne Hill has records going back several decades and at Noar Hill, close-by, there could well be an assembly point.

 

Queen Elizabeth Country Park has had sporadic records over the last couple of decades, but nearby at Lower Harting Down, just on the inside of the Sussex border, I espied a female looking for sallow in 2015, and a male was seen imbibing on the ground on one of my field trips in August 2015. Since this time, other recorders have seen this species grounded and reports have been more common from this site.

 

So I think all in all the Purple Emperor has a rosy future despite some problems with natural forces, which I've no doubt  over thousands of years it has coped with before, and overcome. Unfortunately this doesn't make it any easier to observe, but its enigmatic and mysterious aura keeps us coming back year after year.

 

 

Ashley Whitlock December 2020