PURPLE EMPEROR QUESTION

[Paul Harfield]

Yesterday I observed what I am sure was a female Purple Emperor in an unexpected location. It circled down from the surrounding higher trees and entered a large Sallow. I spent some time scouring the tree from various angles with binoculars and waited, but did not see the butterfly emerge from the tree. Ok I probably missed it but I was just wondering about a couple of things:

This was not in woodland situation, more like a clump of trees. The nearest woodland of any note being about a mile away. How far will female Emperors travel in search of egglaying sites? And how far away from their 'home' woodland will they go?

Once a female has found a suitable Sallow how long will she spend typically within a given tree? How many eggs are likely to be laid by a single Emperor in a given tree?

I would welcome any information on the above. Thanks

[Tony Moore]

I saw a purple Emperor similarly vanish into a Sallow a couple of years ago. I subsequently spent three hours searching every leaf! . I found one egg on the last branch examined...

Tony M.

[Padfield]

I can't answer your questions with definite numbers, but I can add my observations. Firstly, female purple emperors are fussy and lay very sparingly. It is not uncommon to find two or three eggs on the same sapling or bush - more in a larger tree, but not substantially more - but then neighbouring saplings, bushes or trees, which look perfectly suitable to the human eye, will be completely egg-free. Obviously, it's difficult to say this for certain at the egg stage, because any eggs laid more than a few feet above one's head will be almost impossible to spot (they are visible from below as small, round spots, but there are plenty of other things on sallow leaves that appear as small, round spots from below!). But by second instar, caterpillars are relatively easy to detect and in May of the following year they are actually very easy to see even high up in the trees, both by their shadows and by the feeding marks on otherwise fresh, intact leaves. In my experience, they are scattered few and far between. I have often seen females strike trees and bushes that subsequently turn out to have no caterpillars. Now, if we suppose each female lays 200-400 eggs, she must lay in a lot of trees, spread out over a considerable area - and check out many more. My local forest is extensive and contains lots of sallow. My impression is that a relatively small population of purple emperors is scattered over a large area and that the females fly long distances distributing their precious goods. Every year I see one or two in my garden, checking out (and rejecting) my own sallow tree. My house is about 1 km from the nearest place I know emperors to breed - and well out of the forest.

If the sallow your female descended into is suitable (half-shade, with healthy, matt-green leaves &c.) it's worth going back and checking first for eggs, then later for caterpillars. As I say, these are easiest to find in May. Do be careful checking leaves at this time of year. Freshly emerged caterpillars are tiny and inconspicuous - sometimes almost invisible against a slightly spotty or mottled leaf tip. You wouldn't want to brush off a caterpillar inadvertently while looking for eggs ...

Guy

[Paul Harfield]

Hi Tony & Guy

Many thanks for the information.

Looking at other sources this particular Sallow would seem to be in an ideal situation. It is partly shaded and is sheltered by much larger trees. I can not really say much about the quality and type of leaves, I will have to go back and check that. As Sallows go I would consider this quite a large example, most of it out of reach. This particular Emperor event was at around 2pm in the afternoon, I am not sure if that is significant.

I will definitely have a go at finding eggs/larvae, but have no prior experience of Emperor early stages. The information you have given will be a great help. This is a location I visit regularly so hopefully I will have something to report in the coming months, if I am very lucky

[Mark Tutton]

Hi Paul
I have a bit of experience of watching females and finding eggs and larvae. Females, despite their large size, have a habit of both appearing from, and disappearing into, Sallows almost unnoticed - they are very difficult to track once inside but if you are lucky enough to keep your eye on her you will see that she is very manoeuvrable even in quite dense foliage.
As Guy says the normal ( though not exclusive) leaf type is the broad leaved not narrow, pale apple green in colour, with a matt not shiny surface and a 'soft' feel to the touch. The location is in shade, sometimes in very dark shade, either from the bush itself or from surrounding trees. Often the eggs are right inside the bush on a sprig that has a little bit of access around it. They do much more prospecting than laying and as Guy says are very fussy.
The ones I have found have been 2-3m high but I have seen them laid higher.
Once the larvae are feeding the leaf pattern is a good indicator for location, and if the pillar is not present its worth checking to see if the egg base is still present - if so - the caterpillar may well be nearby as they can travel a good distance for such a tiny creature.
I have only ever seen one egg lad in a bush but have found two caterpillars on the same bush but probably by different females.

One from last September

[Paul Harfield]

Thanks Mark

I know it is probably impossible to tell from a photo, but do these look like the correct type of leaves? These leaves are all very soft to the touch and are from the tree where I saw this particular female.

There are actually at least 10 Sallows in this small area all moderately sized trees. Ranging from almost completely shaded to semi shaded. All are pretty much in complete shade from about 4pm at this time of year.

[Mark Tutton]

They look good to me Paul

[Astonvilla]

interesting discussion!
I have been breeding iris since 1983, the first 20 years in Switzerland, where I found it much easier to find the first and second instar larvae, mainly in August.
Back in the UK since 2003, I have found it much more difficult to find larvae, rarely getting into double figures. I am wondering if, in the UK, female iris lays a larger proportion of its eggs out of reach than in Switzerland?
Concerning your female seen a considerable distance from the nearest wood, evidence has been accuulating during the last 10 years or so, that iris is a species not just restricted to woodland, having been found in the wider landscape on many occasions. The female is indeed known to fly out of its birth wood to deposit its progeny further afield: clearly a good survival strategy
Dennis

[Paul Harfield]

Thanks for the info