Evolutionary advantage of blue

[papilio28570]

I try to look at butterfly color and patterns to discern the evolutionary advantage of why that particular color or pattern aided the butterfly to thrive.

I notice that many tropical leps have varying amounts of blue coloration, mostly due to light refraction because so many are iridescent. Does anyone know what the evolutionary advantage the blue color imparts?

Morphos are toxic, so I can see the advantage of being boldly prominent, but what of other genera? I also understand that blue is highly visible in the ultraviolet light-wave spectrum used by leps and this may be advantageous for identifying members of the same species.

So, are blue butterflies all trying to indicate they are toxic to eat...whether true or not? And, why is blue so prominent in the tropics and not elsewhere?

It seems though, that birds would have an advantage as predators since they also see in color and any color or pattern that increases predation would likely be evolved out.

Any thoughts or knowledge out there?

[Chris Grinter]

I'm pretty sure Morpho's are non-toxic, and I know some of their host plants (like Mucuna) are edible. They also have pretty characteristic crypsis on the hindwings and I believe their flight patterns with flashes of blue/UV light make them very difficult to pinpoint in flight. I've also seen them get eaten by lots of birds...

This paper address this topic nicely: www.springerlink.com/content/t830l1427455r140/ (I could try to get the entire article for you at work tomorrow if you're interested).

[saturniidave]

I agree with Chris, the blue on Morphos is a defense mechanism. I have seen footage of Morphos flying and also seen them in Butterfly Houses here and the effect of the blue flashes does make them hard to follow. It is a bit like trying to follow a ball moving lit by a strobe light. For creatures that see further into the UV end of the spectrum it must be even more dazzling when it flashes.

[ruma]

although not quite on topic here, i have noticed that many more neotropical butterflies are very brightly coloured and irridensent with pink, red and blue when compared to butterflies from tropical places elsewhere although there are probably several exceptions. Also african butterflies are generally duller than those of other places.
does anyone know a reason for this?
waz

[papilio28570]

I got the information that Morphos were toxic from this Full WIKI article, 3rd paragraph in Habitat:
www.thefullwiki.org/Morpho_%28butterfly%29

[Chris Grinter]

Huh I don't know how accurate that is - even "regular" wikipedia says they are toxic. I'll try to find something in the literature. But the caterpillars are stunners: myrmecos.net/2011/04/04/monday-night-mystery-24/

[Chris Grinter]

I'll try to track down the entirety of this article, it might help: www.jstor.org/pss/25008804

[saturniidave]

Yeah, I would not hold too much sway with Wickipedia, they frequently get things wrong!

[Adam Cotton]

Surely the green and brown pattern of the Morpho larva pictured in the link in reply #5 is camouflage rather than an aposematic warning pattern, which would strongly suggest that Morpho larvae are not distasteful at all. Distasteful larvae are usually bright coloured, with red, yellow or orange contrasting with darker markings. On the other hand, some larvae which are not distasteful also adopt these general colour patterns.

Adam.

PS. Dave, did you mean Wickedpedia?
It is an excellent resource overall, but needs to be taken with a "pinch of salt".

[lepidofrance]

These caterpillars are Morphos larvae (M. menelaus or M. telemachus ? I found different IDs !). They are in deed aposematic which does not means that they are really distateful or poisonous. As far I know, most of Morphos larvae feed on Sapindaceae, plants which are generally edible with the exception of some of them which are lightly toxic (according "Wickedpedia").

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[lepidofrance]

When you see flying Morphos in nature, we understand how easily they escape predators. First, the large size of some (M. eugenia, M. telemachus) can deter birds. More importantly, the enormous contrast between the upper metallic blue and the dark underside is quite cryptic. The Morpho happens, one first sees a blue glow and then nothing! The Morpho is gone! To reappear a few yards away. Fascinating!

There are however many Morphos damaged. This is due to clashes between males and flights through the branches. However, this female may show the scars of bird beaks?

I add that I never found in the literature mention of the toxicity of Morphos. Moreover, many Lycaenidae are blue and not at all toxic.

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[prillbug2]

It's flash coloration. That's the whole reason for metallic and irridescent coloration. Now you see it, then you don't, because it's meant to confuse predators, including us entomologists. A whole series of papers written on the subject going back at least 70 years ago, by various researchers. It's simply a matter of getting into the library and searching for them.
Jeff Prill

[lepidofrance]

Morphos flying : see :

www.youtube.com/user/pedromariposa#p/u/5/7ATLeuP1JK4

The Morphos from Yungas in Bolivia part1
De : pedromariposa :
The best of my videos of morpho godarti, sulkowski +female and aurora, the sulkowski can be seen at elevations up to 3300m. All 3 species are brilliant metallic light blue and in flight and with sunshine especially the sulkowski flashes golden colour from the underside of their wings.
Fotos here: www.danske-natur.dk/bolivia106.htm

Watch until the end : how Morphos appear and vanish while flying !

Attached picture from the video.

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[jshuey]

Back to the original two points.

I’ve seen plenty of evidence that bird readily eat Morpho helenor in Central America. It’s not uncommon to find “piles” of dismembered wings under presumed bird perches of this species, indicating that some bird is selectively nailing the bug, bringing them back to one spot and eating the body and dropping the wings. I’ve seen this 2 or three times in Belize and once in Chiapas.

Second – why are so many species blue or iridescent? I suspect that there are lots of reasons – but the intense tropical sun has a lot to do with this, especially when you think about the contrast that the deep shade of the rain forest offers. The fact that this iridescence is so easily seen when in the sun from a distance makes it a great signaling tool, regardless of whether you are attracting mates, warning predators, or using it for “flash cryptsis”. Drop that same insect into shade and it is much less visible, especially if it’s a Morpho or Hairstreak that rests with no iridescence showing – it changes from a mirror reflecting the full power of the sun into just another motionless brown “leaf” in the shrubs. It’s a powerful combination for disappearing into thin air.


John

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[starlightcriminal]

Aposematic coloring is a warning for creatures that actually are toxic. Animals that hijack the appearance to suggest danger are mimics- different classifications for mimicry, but Batesian mimicry is what is classically thought of.

Two thoughts on iridescence- the first is that the scales are excited by sunlight and emitting some UV light as a result which is seen by many birds and other butterflies (but not people- this is also true of many iridescent bird markings), so in part it is used as a signaling mechanism, albeit sometimes to predators which is not desirable. The second is that it can function as a disguise in the right scenario. Anyone ever try to watch a fluttering blue against the sky or patchy shade? It's very difficult to keep track of, at least to human eyes which are fairly keen- or mine are anyway, and I suspect it's true of the rest of us bug folks as well.

I have no idea what the evolutionary intention of this device is for certain and I'm sure it varies from taxon to taxon, but I think the explanations provided are correct and pretty comprehensive. I think it is both dazzling and confusing to certain predators in certain situations as well as an attractant and disguise. Think of a peacock, which displays both to impress the ladies and to intimidate would-be predators. They are surprisingly difficult to spot while roosting in a tree- all the little markings and uneven reflections break up their silhouette very well. Most animals don't like to approach something that is doing something new or startling until the learn better. It obviously is a successful adaption, it's not that uncommon in birds and insects at all. Personally, I tend to think it has a lot to do with the UV emissions because it is primarily reserved for organisms that can actually see those wavelengths.