The Purple Emperor ( subsequently referred to as Iris) has been expanding its range northwards steadily during the last 20 years. Last year, it was seen for the first time in south Derbyshire, and in 2025, several other sightings weremade in the north east of that county, possibly as a result of expansion from nearby Sherwood forest. It is seen frequently in Nottinghamshire and Leicestershire these days.

In Yorkshire, two were seen in Maltby Wood in 2016, but none since; also, several years ago, a female was spotted in the heavily wooded Oughtibridge area on the north western edge of Sheffield: again, not seen since. This year, four records were obtained: They were  the eastern edge of Middlesborough, at two locations near  Guisborough woods.  Askham Bryan Wildlife Park a few kilometres west of York. Lastly at YWT Sprotborough Flash on the Don near Doncaster. 

This species favours woodland with plenty of Salix. Most used is  Salix caprea, Goat Willow, with broad leaves, although teh very common narrower leaved hybrids (with Grey Willow Salix cinerea )are used too.  These sightings may be the result of releases, although the fact that they  were far apart suggests otherwise. For a species to establish itself, it has to breed, so we need evidence of this and your help.

To increase confidence that this species has reached Yorkshire, evidence for breeding is needed by searching for hibernating larvae so we need your help. 

One strategy is to search for hibernating larvae during the winter on Sallow. This is difficult, since they are superbly camouflaged (see the images below).

The most successful method is the so-called dangle leaf method. An image below the larva while still on a leaf spins a silk pad at the point where the leaf stalk is attached to its twig; this ensures that the leaf does not fall to the ground with the larva. Eventually, the larva will leave the dead leaf and take up a position, usually near a bud, usually not further than about 3 metres from the leaf.

When most of the leaves have fallen during November, the dangle leaves, still attached, will be easy to find. This is when you should look for larvae. There are two dangle leaves images: one shows a leaf hanging by a long thread, which is unusual. The other image is commoner, with the dangle leaf attached close to its twig.

A great deal of patience is needed: there is no point searching woods which do not have plenty of Sallow. 

Matthew Oates' “His Imperial Majesty, a Natural History of the Purple Emperor” is a must have book for anybody who wishes to learn as much as possible about this iconic species.

This is an arboreal butterfly, spending a great deal of its time perching high up in various trees. You need binoculars always, although scanning the trees in my experience does not generally lead to success.

Reading old books leads us to believe that the Emperor is confined to Oak trees, and to a lesser extent, Ash. The experiences of the last 30 or 40 years now indicate that it can be found on and around most deciduous trees, and even conifers such as Scotch and Corsican pines.

Matthew Oates maintains that it is a landscape species, often to be found away from its main habitat, woodlands, in more open areas, such as copses along high ridges on the south downs for example. The presence of Sallow, preferably Salix caprea, is very important.

The seasons have been getting earlier; in the south they start looking from mid June: here in Yorkshire you can start in late June, with the peak in mid-July. In a good season, they will be seen into August, the flight period being five to six weeks.

On a sunny warm morning in July, we start our search from about 10 am, but on hot days [25oC plus], they will be active earlier. The males, early in their life, often descend to ground level where they can be seen probing stones and gravel. There is a theory that they are imbibing salts to build up their strength prior to mating. Dog and fox faeces are a favourite delicacy, and they often remain on excrement for many minutes. They rarely take nectar from flowers, but we do have quite a few examples, of females especially, on buddleias : in fact, this season a female was photographed on buddleia at Sprotborough Nature Reserve near Doncaster. People have used various methods to bait Emperors, and the most successful to date is diluted oriental shrimp paste: this has the most disgusting smell!

Find a wood in your neighbourhood which has lots of Sallow: as mentioned, a vital ingredient for success. Visit on a sunny, windless day in July, armed with binoculars, and wander slowly down a wide sunny ride, scanning the trees and paying attention to the ground in front of you. They often take to the wing for short flights between canopy gaps and they are easy to miss, so patience is a virtue. Early in their life, males adopt a strategy of Sallow searching, looking frantically for females which have just emerged or about to emerge. If you are lucky enough to go out on such a day, you will experience this extraordinary behaviour of males flying rapidly in and out and around the Sallows.

The other typical male behaviour is Oak edging: they fly at mid tree level along a line of Oaks at the edge of rides, probably also searching for females. On very hot days, it is not recommended to search in the afternoon, when they became rather inactive, flying again from about 5 pm onwards.

Perhaps the most exciting aspect is observing males clashing above the trees: they are extremely territorial, and when another male invades their space they will engage, resulting in wonderful aerial battles: both spiralling high into the sky until the victor returns to his perch. It is thought that the perching strategy allows them to look downwards for any females which may be passing.

In undulating woods, it is well established that the male will seek out a group of trees to use as territory at the highest point in the wood; as long as there are a number of trees here, several males will be in occupation and it gives the best chance of observing behaviour. In a flat wood, a group of the tallest trees will be used. In Waterperry Wood Oxfordshire, for example, which has no clear high point, the males can be seen year after year on and around a clump of tall Ashes Oaks and Poplars.

The females are much larger and do not have the purple iridescence; they tend to fly at a lower level than the males, spending most their time in and around the Sallows. They can remain immobile for very long periods; for example, a nature reserve warden in Buckinghamshire had set up his telescope with camera attachment to observe birds. By chance, he saw through his scope a female Emperor near the top of an Ash tree; he remained there for 6 hours before going home: the Emperor was still there!

Interestingly, they are often attracted to ‘foreign objects’ within their territory. Examples are cars, isolated buildings within or on the edge of woods, and people: they will often ‘buzz you’ and even land on you; I have plenty of photos of His Majesty on people.

The Purple Emperor has been spotted at four different locations in Yorkshire in 2025: this is very exciting. The more people who go out looking in the right habitats, the more chance we have of understanding about the distribution in Yorkshire.

Good luck!

Dennis Dell