Purple emperor butterflies (Apatura iris) are one of the most sought-after butterflies in the United Kingdom and considered rare finds for many enthusiasts. While they may not be as rare as some people believe, their elusive nature and specific habitat requirements do make sightings a special occurrence.
Background on Purple Emperor Butterflies
The purple emperor is a medium-large butterfly found across parts of Europe and Asia. In the UK, it is primarily restricted to southern and central England. Adults have velvet-brown wings with striking purple iridescent markings on the upperwings of the males. The underside of the wings is light brown with prominent white streaks.
These butterflies live in oak woodlands and are dependent on oak trees for their entire lifecycle. The caterpillars feed on oak leaves, while adults get most of their nutrition from honeydew secreted by aphids living in the trees. They occasionally visit flowers to drink nectar.
Purple emperors have a relatively short flight period, emerging as adults in early July and dying out by early August. The peak is around mid-July, but can vary in different years and sites. They are active during sunny, warm weather.
Why Are They Considered Rare?
There are a few reasons why purple emperors have gained a reputation as rare and elusive:
- Restricted range in the UK – They are only found in southern and central England, within the range of oak trees.
- Short flight season – With just 4-6 weeks as an adult, they are only on the wing for a brief period.
- Specific habitat needs – Dependence on oak woodlands limits where they can survive.
- Wariness – They are extremely sensitive to disturbance and will rapidly fly up into the treetops.
- Roosting habits – Adults spend much of their time high in oak canopies, out of view.
- Unpredictable emergence – Hot sunny weather is needed for them to fly, so their daily appearances are erratic.
- Unsuccessful searches – People often go looking for them at the wrong sites, times of day or weather conditions.
These factors combine to make purple emperors a challenge to observe. Even at sites where they are present, you may go multiple times and not see any if the conditions aren’t right.
Population and Conservation Status
The population of purple emperors has likely declined over the past century due to habitat loss, but they remain widespread across their historic range in England and Wales. Accurate population monitoring is difficult due to their ecology, but there is no evidence they are threatened with extinction.
They are considered a Priority Species in the UK Biodiversity Action Plan and a Species of Conservation Concern in England. These designations recognize their dependence on vulnerable oak woodlands. Their main threat is further habitat loss and fragmentation as old oaks are removed.
While they have disappeared from some historical sites, purple emperors persist in well-managed oak woodlands. Improved awareness and targeted conservation efforts at key sites have likely aided the stability of their population in recent decades.
| Conservation Status | Classification |
|---|---|
| IUCN Red List | Least Concern |
| UK BAP priority species | Priority species |
| England NERC S41 | Species of Conservation Concern |
Finding Purple Emperor Butterflies
Looking for purple emperors requires patience and knowledge of their habits. Here are some tips to improve your chances:
- Search established oak woodlands, not isolated trees or hedgerows.
- Time visits for warm, sunny, breeze-free days in mid-July.
- Focus efforts between 10am-3pm when they are most active.
- Walk slowly, scanning treetops around oak canopies.
- Watch for aerial pursuits between patrolling males.
- Try locating fresh oak sap runs to find where adults gather.
- Don’t disturb adults that come down to ground level.
- Use binoculars and photographers should use long telephoto lenses.
Purple emperor hotspots that are publicly accessible include Bernwood Forest, Bookham Common, Chappetts Copse, Collins Copse, Daneway Banks, Finemere Wood, Glapthorn Cow Pastures, Oaken Wood and Whitecross Green Wood.
Rarity Among UK Butterflies
There are 59 regular breeding butterflies in the UK. Based on distribution and population levels, purple emperors rank somewhere in the middle for rarity according to the following classifications:
- Extinct – Gone forever, no individuals left (e.g. large tortoiseshell)
- Critically endangered – Extremely close to extinction (e.g. large blue, black hairstreak)
- Endangered – Very high risk of extinction (e.g. wood white)
- Vulnerable – High risk of extinction (e.g. Duke of Burgundy, high brown fritillary)
- Near threatened – Risk of becoming endangered (e.g. white-letter hairstreak)
- Least concern – Widespread and plentiful (e.g. meadow brown, gatekeeper)
The purple emperor is in the least concern category along with the majority of widespread, successful butterflies. However, its specific needs and limited range in the UK will likely always make it one of the more sought-after species to observe and photograph.
Conclusion
In summary, purple emperor butterflies are considered rare in the UK due to their elusive habits, specific oakwood habitat requirements, and relatively short flight period. They are, however, not globally threatened and remain widespread across areas of southern England and Wales where oaks occur. Their populations appear stable, especially on protected sites. Seeing one is a prized natural history experience that requires timing, luck and patience, but purple emperors are not as rare as some believe if you visit the right locations at the peak of their flight season.
