Wing-roll behaviour of some members of the Lycaenidae family

[ernie f]

the bird sees the movement and has to make a split second decision into the most likely position of the head. If it pecks at the wriggling hindwings then the butterfly is more likely to survive.

Yes! I am coming round to your view (and CallumMac's). What you say is a very convincing scenario for me. The bird is more likely to choose the bit that's moving.

The fact that Chalkhill Blues don't seem to do it is therefore largely irrelevant. They never evolved the behaviour for some reason, that's all.

[Jack Harrison]

I have seen the delightful Common Posy in the Far East
http://www.butterflycircle.com/checklis ... 200908.jpg
and I am sure I witnessed that wing movement.
With the long tails waving about, that must be a huge advert to birds: "this is the right place to attack."

Distraction hypothesis has my backing.

Jack

[ernie f]

Right - so I've given it a lot more thought and now I am totally convinced.

The Wing-roll as a predator deception mechanism – a summary

I have seen a newly emerged Silver-studded Blue hop up from its ant-attended position on the ground onto a heather bush and immediately do a wing roll. I was standing beside it all the time it was on the ground and while it was on the bush. It did not do the wing roll on the ground so it did not consider me to be a threat but nevertheless it did the wing roll on its first perch. I have seen other species do a wing-roll immediately on first perching after flight - for example Small Blue, Brown Argus, Common Blue and Holly Blue. In every case there did not appear to be a threat. I have seen one land within a few inches of me and do a wing-roll. It is not therefore necessarily doing a wing-roll actively to distract a predator that it knows is near. It is an action that is more passive than that. It is done automatically to attempt to deceive a potential predator when the butterfly is prone to a potential threat. For example on first landing.

I have seen a female Silver-studded Blue on the ground in a wide-open habitat doing a wing-roll for a long while and with a higher than “average” frequency, while at the same time nearby to her I have seen a male on heather resting and doing it in a more leisurely fashion. In this case it appears that the more prone to predation the butterfly is, the more it performs the action, both in duration and frequency.

I have noticed that if a butterfly knows it is under threat it will just fly off. I have regularly approached Silver-studded Blues from behind and they do not realise I am there. I can even do it from about ¾ behind. But if I approach from the front or at an acute angle to the front, it will see me and fly off. The fact that all the butterflies that do the wing-roll do so with their rear wings while (with varying levels of success) keeping their body and front wings still means that a bird that they cannot see approaching from behind will be attracted to the rear-wing movement and will thus peck at the part of the butterfly that is nearest to them - the rear wings. As Bugboy rightly points out, most birds are attracted to moving things as prey (we can ignore scavengers in this scenario).

If the bird approached from the front, the butterfly merely flies off. The rear-wing roll therefore has evolved to direct the predator to the least vulnerable part of the butterfly when the butterfly cannot see the predator approaching from behind. Somehow it is making changes in this tactic dependent on how prone to predation it is at any given moment too. This explains why they can sometimes go a long while without rolling their wings. The energy expended in performing the wing-roll is therefore regulated and energy conservation is optimised. I do not suppose for one minute the butterfly is making conscious judgements about this – somehow it is an automatic mechanism that automatically changes in duration and frequency as a response to the changing environment around it.

The fact that some species have a special adaptation where at the apex of the roll they slightly part their wings may be an additional means by which they can direct the bird to the rear-end. Consider if the bird approaches precisely from behind. If the wings of the butterfly are closed and it wing-rolls only along the body axis, then the wing-roll becomes invisible to the bird and the effect is totally negated. But if the wing roll also has a sideways component it will be seen as movement by the bird from any angle it happens to approach from. Some butterflies, again like the Silver-studded Blue, can do the wing-roll with wings open or ajar which of course then exaggerates the sideways component even more.

Rear-wing tails and eyes are a completely separate evolutionary development, a second way of deceiving the predatory bird. They have to be because many Blues don’t have them. Obviously the eyes and tails (meant to imitate antennae) are to make the bird think it is aiming for the front of the butterfly when it is actually the rear. At some point down their evolutionary history, some butterflies got both the wing-roll behaviour and the eye or tail markings together and each mechanism supported the other to protect the butterfly even more.

The fact that some butterflies in this family don’t wing-roll only means that certain species did not evolve in that way. In the same way that some in the family did not evolve “tails”.

[ernie f]

Great picture Jack. It really does look like it has two heads. What all other butterflies should aspire to.

[Jack Harrison]

Oh, that wasn't my photo although I do have some old slides but nothing like that quality. I saw them in Singapore in the early 1970s in a small remnant area of rain forest and didn't at the time know what they were called. They were certainly impressive.

Your analysis of the of the Lycaenid behaviour omits one obvious explanation: they are simply scratching their itching wings

Jack

[Goldie M]

I'm no expert on any thing like this But when the these Butterflies you speak of arrive in my garden I watch them closely as well as taking Photo's and I came to the conclusion it was all down to balance, I just assumed that because they're so delicate they did this wing roll to stay balanced, much like the Birds do with their wings when it's windy, I watched a Blackbird on my fence this morning in the strong wing opening and closing it's wings to stay balanced on the fence and the thought occurred to me that maybe the Butterflies did the same, just a thought.
I always thought birds look out for movement when wanting food, I know birds of prey do! wouldn't move meant of their wings attract the birds, again just a thought! Goldie

[ernie f]

Jack and Goldie - I just love all this too-ing and fro-ing of ideas. I think its great fun trying to suss out why any animal does any behaviour.

I love your scratching thing, Jack. In the Broxhead Silver-studded Blue lek there is always a lot of scratching going on amongst them!

I like your ideas too Goldie. Keep them coming. Although I may now be convinced about why they do it, for me it is only a belief - I have found no published scientific proof that I have not been able to argue against.

Regarding balance though - I have seen a female firmly standing on the ground - no breeze about to destabilise it, doing the wing-roll rapidly and continuously for some while. I think without rolling her wings she would have balanced OK in this situation. Also I think the idea is that they roll their hind-wings to attract potential predators to that end thus allowing the butterfly to escape an attack should it occur. The reason why Bugboy convinced me is because I have seen this behaviour occur mostly when a butterfly has been in flight and then perches. If a bird had been stalking it while the butterfly was in flight, rolling the back wings for a while when first landing would distract the bird to peck the "safe" bits.

Nevertheless, I am always open to other suggestions.

[ernie f]

I have just been skipping through one of my butterfly books, more or less at random and came across this for Peacock Butterflies.

Quote: "Adults flash their wings at potential enemies, using its "eyes" to warn them off. It can also rub its forewings and hindwings together to generate a warning sound".

Cripes - now I am waiting to see more Peacocks to see how they rub their wings together because I have never noticed it before.

[Goldie M]

I saw a program once about the Peacock Butterfly ernie, it showed the Peacock in Hibernation, it was dark and in the same hole as a Mouse , where ever it was, I've forgotten, any way the Mouse was going towards it when suddenly it flashed it's wings open and it used the two eyes on it's wings to scare the mouse a way The Mouse thought it was a predator
I really can't remember what the program was called but I'm sure other people must have seen it as well at some time.
If your book says the Peacock moves it's wings has a warning, looks like other Butterflies do the same. Goldie

[ernie f]

Goldie - I pity the mouse!

... and what interests me is that the wings are supposed to make a sound when the Peacock rubs them together. I wonder if others that rub their wings together are also making a warning sound?

[ernie f]

I visited the Broxhead Silver Studded Blue colony today which is reaching its max count but I was not there to count them. It was overcast, a bit cool at 15 degrees and with a slight breeze between 10 am and 11 am. I stayed in the lek area and found about 50 males. Some were in their roosting position but many were flitting about. Of the 50 seen only one did a wing roll and I was there for about an hour scrutinising them through field binoculars and even sometimes getting quite close, around 3 cm away. He did it with wings wide open for about 40 seconds then he stopped and although I was with him for at least 5 minutes he never did it again. He was a very fresh individual. Pictured below.

Normally this bunch of butterflies do a lot of wing-rolling so I wonder whether temperature might also be a factor in their ability to do it - that is If they do not have sufficient stored energy.

[ernie f]

Today at Broxhead between 9 and 10 am there were 90 SSBs in the lek of which 9 were wing-rolling (8m and 1f). It was overcast with a very slight breeze but the temperature was 18 degrees C. Many of the butterflies were quite active despite the lack of sun. 7 pairs in the lek were mating for example.

[dilettante]

One other thing to throw into the mix: there's been a lot of discussion about distracting bird predators, but let's not forget other predators. Crab spiders for example, or mantises, or lizards. Maybe some of those don't need false eyes (eye-spots) or antennae (tails) to be sufficiently confused to strike at the wrong place.

[ernie f]

dilettante - a very good point. there are a lot of reptiles at Broxhead heath. Indeed I have seen many Common Lizard nearby and on occasion even a Sand Lizard.

[ernie f]

Today the Broxhead Blues where doing quite a lot of wing-rolling. It was 21 degrees C, mainly overcast but with some sun and a light breeze.
Both males and females were at it, wings open, ajar and closed. One female was really going for it. Not only was she wing-rolling her hind-wings and doing the usual parting at the apex of the roll but the front wings were also parting slightly on each cycle of the roll. I had not noticed this before so I looked for it again, and found a male doing exactly the same nearby.

[ernie f]

Today I went to Daneway Banks for the Large Blues and saw one do a wing-roll, first with wings closed and then with wings ajar.

I saw a couple of dozen individuals in total while there but only this one was doing it.

[dilettante]

So another thought, based on the observations of wing parting. Could it be to realign scales, like a bird preening its feathers? For blues in particular with any sort of irridescence, I'd imagine having well-aligned scales would be a good thing for maximum effect. I've no idea if scales get misaligned (rather than just dislodged), or could be realigned in this way though!

[ernie f]

Dilettante. I like it that this topic is still being brainstormed because I don't think we have entirely bottomed it out. Your preening idea is great.

When I first saw this activity - it was with the Silver-studded Blues, I immediately thought that because the wings sometimes parted at the apex of the roll, they were purposefully rubbing scales off for some reason. The fact that this butterfly has darker bands just where the wings are rubbed together seemed to support such a notion. Most of the other butterflies that do it also have a darker band where the wings rub together. I say "most of" because I can't tell if the Small Blue has such bands or not and it is certainly capable of doing wing-rolls.

I was becoming a convert to the passive predator redirection theory but I started to question it again when I saw one butterfly species move its fore-wings at the same time as it was rolling its hind ones.

Also some-one on this forum (sorry I forget who) suggested that merely making such a movement was broadcasting their presence to a potential predator. Keeping still would work better one might think. In fact when I approach any butterfly species to get a close-up photo they seem to employ one of two strategies when they know I am there. Either they freeze or they just fly off. Sometimes they do both - freeze momentarily and then scarper.

Also recently, of the hundreds of Silver-studded Blues I have seen, although a lot wing-roll, it is still a fraction of the total. Of course you cannot see them all, all of the time, but if it was solely down to predator evasion, you might have thought most would be doing it most of the time. The counter argument to this is that they might do it more if they think they are at greater risk. Most of the SSBs I have seen are in a densely populated lek situation. If they consider they have safety in numbers they might not need to do it quite as much.

But to summarise my view - first I did not think it was for predator redirection, then I did, now I am tending to sit on the fence and take an objective, observational view. In other words I am collecting the facts as they present themselves and see where this leads us.

There is no doubt in my mind that those species that have antenna-like "tails" or hind-wing "eyes" which also do the wing-roll, gain predator evasion benefits from the action, but it may well be that the wing-roll serves an additional purpose and its predator evasion value is secondary.

I would be happy for you (and anyone else of course) to add to this discussion topic with any field observations they have made about wing-rolling as well as brainstorming ideas about its purpose.

[millerd]

Just to add to the mix - a lot of the WLH I saw in Essex on Saturday were indulging in this behaviour. However, I couldn't work out any common factor to it. Several were landing, rolling their wings then walking between bramble flowers and doing it again.

Cheers,

Dave

[ernie f]

Dave - Yep - That's just what the Silver-studded Blues do, except mainly on the heather rather than bramble because that is their preferred plant but I have also seen them do it on the ground.