Natural History Photographs

by Cor Zonneveld

Some thoughts about the colours of Butterflies

General

Butterflies are very popular insects, no doubt in no small part due to their beautiful colors. Although as a group they have more colors than the rainbow, some themes can clearly be delineated. In this page, I try to say something about these themes. First of all, many groups of species clearly share a basic color pattern. Such groups are often quite comprehensive, subfamilies or even families. Their vernacular names makes already clear what the basic color pattern is: whites, yellows or sulphurs, coppers, blues, and browns. Here are some typical examples, to show that these names are aptly chosen indeed.


Black-veined White: Aporia crataegi	Clouded Yellow: Colias crocea


A copper: Lycaena ochimus	A blue: Polyommatus semiargus


Meadow brown: Maniola jurtina

If you visit the pages for the families, you'll notice that family resemblance is quite strong indeed. Whites are predominantly white, with various amounts of blackish, greenisch or orange patches. Browns are mostly brown, with orange, and white-pupilled black eyes. The strong resemblance is due to their evolutionary relatedness. The whites share pigments that must have been present in the ancestor of the whites. Yellows (also called Suplphers, but since sulpher is very yellowy, this amounts to much te same) likewise share pigments that must have been present in the ancestral sulphur. But although blues do share a common ancestor, it hadn't a blue pigment! Neither does any blue flying around now has blue pigments. The often brilliant blue colors have a different origin.

Pigmental versus Structural colors

Butterfly scales may have color because chemicals present in them absorb specific wave lengths of the visible light, and reflects others. Depending on what wavelengths are absorbed and reflected, different colors are observed. But in many species the colors we observe are produced not by pigmentation but by the interference of light due to multiple reflection within the physical structure of the scales that cover a butterfly wing. For this reason they are referred to as structural colors. Besides the Adonis blue above, I'll show some more examples.

Green hairstreak, Callophrys rubi. The green color is certainly a structural color; green is never a pigmental color in butterflies. The upperside of the wings is brown; it can just be seen because the butterfly rubs its wings in contrary motion, exposing a small part of the wing's upperside.	The Purple Emperor, Apatura iris. One of Europe's finest butterflies! This photograph shows that the blue color is structural rather than pigmental; the blue reflection is dominant on one pair of wings, but almost absent on the other. The effect of iridescence cannot be seen under certain angles, as explained in "Now you see it - now you don't"

Queen of Spain Fritillary, Issoria lathonia. The mother of pearl patches are structural colors, the orange and browns are pigmental.	Erebia tyndarus. Many browns have some reflection colors if they are very fresh, but the effect is rapidly lost. The brassy ringlets (Erebia tyndarys group) show particularly rich reflection colors; here you can see blue and green.


Lycaena helle. Reflection colors are an add-on, as can be nicely seen in this copper: on top of the 'normal' orange and brown pigmental colors, there is an overlay of purple reflection. But not all scales give rise to reflection: a small rim of the forwing, close to the outer margin, is not reflective, as well as about half of the hind wing.

Functional aspects

Biologists tend to think that many attributes of an organism are adaptations. This is a notoriously difficult notion, which we shall not drift into. But one aspect of adaptations is quite easy to understand: if something has to count as an adaptation, then it should clearly enhance the survival chances of the organism. What about butterfly colors? Are they "for" something? This is rarely easy to determine. In fact, one should experimentally show that a particular aspect of coloration enhances the survival of its bearer, something thas has rarely been done. I only know of one article, Intimidating Butterflies. The butterfly in question is the Peacock. Its eyes apparently frighten potential predators. The author of the paper concludes that "the eyespots function to dissuade the bird from pressing home an attack. It also appears that this is achieved by a bluff..." Here are some photographs of the Peacock (Inachis io). The photograph on the left tells a slightly different story, although the outcome is the same: they eyes appear to enhance survival.

How did the damage on the butterfly's wings came about? Did the bird attack an eye? Unlikely, in view of the symmetry of the damage; the bird must have attacked the butterfly when it had its wings closed. But the butterfly opening its wings, showing the full splendour of the eyes, must have been too much for the bird's gusto. Startled to death, it must have let the butterfly escape. I once saw our cat at home touch a Peacock with wings closed. The butterfly opened its wings suddenly, and our cat jumped 1 meter backwards, from rest!

Just in case you didn't notice: I'm not here...

But although solid evidence about the fucntional aspects of coloration is often lacking, one can surmise some reasonably plausible hypotheses about it. Take for instance avoiding your predator by trying to blend in with your surroundings. The technical term for this is crypsis. Cryptic coloration can certainly explain some patterns observed in butterflies. Look at these examples:

Hipparchia semele - Grayling	Hipparchia statilinus
The Grayling in the photograph on the left is difficult to spot. The effect is greatly enhanced when a big butterfly like the grayling suddenly drops out of flight and settles on the ground! The Graling in the right photograph is more conspicuous, but imagine you are looking in a sea of sand for a slightly differently colored grey... As these butterflies rarely if ever expose there uppersides, they are well protected even if they are active. However, some species combine cryptic coloration on the underside with flamboyant colors on the upperside. They will be cryptically protected when at rest, but not when active. Examples are the Peacock above, and the Small Tortoiseshell:

Aglais urticae - Small Tortoiseshell

Does the white band signal presence or absence of its owner?

A white band across the wings is a feature observed in many European butterflies in the families Nymphalidae and Satyridae. Here are some examples:

Limenitis camilla - White Admiral	Apatura iris - Purple Emperor
Two butterflies with similar colour pattern, and similar bird-attack marks. Coincidence? My hunch is that this colour pattern is functional in woodland area, the habitat of both species. Both species often rest on branches and leaves, in sunshine. There is often an extreme contrast between full sunshine and deep shadow, as can be seen in the photograph of the White Admiral. To a bird, the white band may every now and then appear as bright patches of sunlight, in effect hiding the butterfly. An alternative explanation is that the white band is the focus of an attack, because of its visibility. This perhaphs better explains why both butterflies exhibit bird attacks marks at the white band! Obviously, to distinguish between the two hypotheses one has to do some delicate experiments....

Fake antennae?

A similar argument if often put forward to explain the threadlike filaments at the hind wings of Hairstreaks. These would be similar to the antennae, in fact creating a 'false head'. Because hairstreaks habitually rub their hind wings, the swinging filaments might atract a bird's attention. Here are two photographs of a the hairstreak, Satyrium spini. The white tip at the end of the filament certainly draws attention, may be more so than the real antennae. The photograph right shows a sizable gap at the place of the filaments, consistent with the idea that the filaments draw the bird's attention away from the more vital head...

Satyrium spini

I'm warning you! I taste bloody awful!!

Above we have seen two general strategies: The Greyling aims to distract attention, it aims not to be seen. The hairstreak aims to distract the bird's attention toward the less important wing filaments. The opposite strategy is to attract attention of potential predators, but to fool them at the same time. This strategy is followed by the Peacock, which attracts attention with its eyes, to fool the bird. The strategy of attracting attention is also followed by butterflies that are distasteful. They advertise their distastefulness by so-called aposematic coloration. Aposematic coloration consists in bold patterns of the colors white, red, yellow, black and blue. Here are some examples:

Parnassius apollo	Zerynthia rumina

Zygaena purpuralis