Function of eyespots in butterflies, part 1: apollo butterflies

 (writing in progress) 

How do eyespots in butterflies function?
 
There is a considerable literature on this topic (e.g. please see Stevens M 2005 Biological Reviews, on eyespots in Lepidoptera). However, the question remains. 

Going back to basics:
 
Many butterflies, and a few moths, are certainly aposematic, i.e. they have gaudy/garish/ominous/pointed conspicuous colouration which – regardless of any attraction between the sexes of the butterfly concerned – serves as a clear warning to predators: ‘I am toxic’.
 
However, I do not see eyespots as part of this syndrome.

Eyespots can certainly deter predation. However, this by a different psychology: that of confusion, and implication that the butterfly is instead a larger, unidentified, and threatening animal.

I would not call this function of eyespots ‘aposematic’. Aposematism is essentially an honest communication (although it is dishonestly mimicked by many butterflies, and there is an almost obsessional literature on that which has grown so large that I sometimes think it blocks many from going back to common-sense basics).

Eyespots are not the same: they are neither honest (nor a form of mimicry in the same sense as aposematic mimicry, because there is no real model and the vague model is not toxic), nor a warning sign of some special defensive capability. And the best examples of eyespots in Lepidoptera occur on otherwise camouflaged species, including some moths.
 
In short, eyespots in butterflies qualify neither as ‘warning colouration’ nor a sign of special defensive capability. They deserve a name other than aposematism.

Can readers think of a suitable name for this defensive syndrome?
 
Now, coming to apollo butterflies (Lepidoptera: Papilionidae: Parnassius) because they exemplify the confused thinking out there:
 
Please see the account in Wikipedia below.
 
We know that apollo butterflies are toxic (much like a familiar confamilial in Cape Town with black-and-cream spotted markings, the African citrus swallowtail Papilio demoleus), and that their caterpillars are aposematic, so it’s fair to expect the imagos to be aposematic. And they certainly are conspicuous butterflies (collected virtually to the point of extinction for this reason).

So far so good. But what on Earth could the ‘eyespots’ achieve in this case?
 
Please look at some photos of apollo butterflies for yourself (a few examples from Wikipedia below). How on Earth could these small ‘eyespots’ possibly fool any would-be predator into thinking that there is some larger animal staring at it? It just doesn’t work in this context. Aposematism and eyespots just are not compatible, are they? Particularly when the eyespots are so small and numerous on an already vivid, conspicuous wing. And on both sides, inner and outer, so there’s zero surprise value involved. The ‘eyespots’ aren’t even big enough to intimidate anyone.
 
Ask yourself: would the garish effect of the colouration of apollo butterflies look any less sinister without the eyespots?

My answer: perhaps, but not because they resemble eyes, just because the pattern is so bold (with tonal contrast as well as the vivid hue of red) that the would-be predator would notice that this pattern makes no attempt to be disruptive (= inconspicuous). Other geometric patterns would look equally suspect = ominous.
 
My interpretation:
 
I would not call these features of apollo butterflies ‘eyespots’. I think several different patterns are being conflated under ‘eyespot’ in Lepidoptera at the moment. I doubt that any would-be predator ever looks at an apollo butterfly and thinks ‘Heeby-jeebies, there’s a big animal suddenly staring out at me where I expected only a tiny vulnerable insect to eat’. No would-be predator ever thinks ‘yikes, that’s an eye staring at me’. All they think is ‘that butterfly is advertising itself, a sure sign that it knows I’ll suffer if I eat it’.
 
There is of course at least one other syndrome in butterfly colouration, in which tiny eyespots on the posterior of the wing may distract a predator to strike away from the head. But there again we should not be calling those features by the same term we use for the big, confusing/startling, frightening eyespots that we see in several lineages of both butterflies and moths.
 
Eyespot, in summary, has become meaningless and we need new words. We need to come up with these new terms. Otherwise, the question ‘what are eyespots in Lepidoptera for’ becomes meaningless = unanswerable, surely?
 
And there is also another dimension to this, not even mentioned below in Wikipedia:
Given that many other animals see ultraviolet, how do we know that what the human eye sees as an ‘eyespot’ in an apollo butterfly even resembles an eye to the most important predators involved?

http://en.wikipedia.org/wiki/Apollo_(butterfly)

http://en.wikipedia.org/wiki/Apollo_(butterfly)#mediaviewer/File:Apollo_butterfly.JPG

http://en.wikipedia.org/wiki/Apollo_(butterfly)#mediaviewer/File:Papilionidae_-_Parnassius_apollo.jpg

to be continued in https://www.inaturalist.org/journal/milewski/68255-function-of-eyespots-in-butterflies-part-2-peacock-butterfly#...

(writing in progress)

Posted on 16 de julho de 2022, 03:07 AM by milewski