The Map; in red and black

A bright orange Araschnia levana bathing in the spring sun

The Map Butterfly (Araschnia levana) is one of those small spring butterflies that emerge near the end of april and throughout may. While the red and black colouring on the upperside of the wings slightly resemble that of the Small Tortoiseshell (Aglais urticae) or Comma Butterfly (Polygonia c-album), it sports an underside unlike any other. Different shades of brown, orange and purple, traversed by a fine network of pale light veins, this beautiful mosaic gave rise to its common name the Map Butterfly.

The unique underside of the Map Butterfly (Araschnia levana)

The Map Butterfly (A. levana) has two generations a year in Denmark, with the second generation emerging in July through August.
Denmark is within the Map Butterfly’s (A. levana) more northern area of distribution, and it is only within the last 30 years or so that it has colonized Denmark completely. It is pretty common in most of Europe, though very rare in UK. It has been attempted introduced to the UK several times, failing each time. *In 1912, following an attempt to introduce the species, a persistent fellow, was so opposed to the introduction, that he spent a summer catching and destroying every single individual he could lay his hands (or net) on. The introduction failed, and though he undoubtedly claimed his victory other factors have been decisive.
Nowadays it is very rarely seen in the UK, with a few migrating individuals observed on the south-eastern tip, now and then.

The Map Butterfly (A. levana) is a butterfly, studied to detail. The reason for this? Here’s a picture of a typical second generation Map Butterfly:

The dark summer morph of the Map Butterfly (Araschnia levana levana f. prorsa)

It’s still a Map Butterfly, though it doesn’t look at all like the orange spring one shown at the beginning of the post.
The Map butterfly occurs in two different forms, the spring orange and the summer black. The undersides of the two morphs look much more alike (not to say are more or less identical). This black summer morph is named Araschnia levana levana f. prorsa, where the spring morph would correctly be Araschnia levana levana f. levana.
The phenomenon is called diphenism, and covers morphologically alternating forms of a species determined by environmental factors, in this case something related to seasonality.
Chances are, if you are a butterfly enthusiast, entomologist or biologists you have, at least peripherally, heard about this butterfly as it is a classroom example of diphenism, and one of the most extreme examples.

First need-to-know thing is this; at the end of the season the larvae of the Map Butterfly pupate and hibernate through winter, thus overwintering as a larvae inside the pupae. When spring arrives, levels of hormones trigger the metamorphosis and the change from the larvae into the adult begins.

The newly formed adults emerge in end April / beginning of May, all red spring morphs. They mate and deliver the next round of larvae.
Now this round of larvae DON’T enter into a state of hibernation. Instead, once the pupae is crafted the change to adult begins almost immediately. Well, within a matter of a day or two that is. These larvae give rise to the black f.prorsa generation, emerging through July and August.

The obvious difference here, would be some larvae begin the change to the adult almost immediately after pupating, resulting in black butterflies, whereas others take a good long winter nap inside the pupae, before changing into butterflies. Orange butterflies.

The strongest factor affecting whether the larvae enter hibernation or not, is day length during the development of the larvae. Larvae that have developed during long days, increasing daylight, skip the period of hibernation, whilst larvae developed during short days, decreasing periods of daylight, hibernate. Indirectly photoperiodic lengths are affecting the occurrence of the two morphs. The direct cause though, has been found to be the hormones involved in kickstarting the development of the adult butterfly, specifically ecdysteroid.

Ecdysteroid is released initiating the change from larvae to adult. If this release occurs in the larvae within the first two days, a dark summer morph f.prorsa results. If the release occurs longer than 5 days after creation of the pupae, the red spring morph f.levana emerges. If the release occurs between 2 and 5 days after creation of the pupae, as arranged in the lab, an intermediate morph is the result.

As to the use of these two differing morphs, there has been quite alot of speculation.
Changes in morphological appearance by coloration and patterns often serve one of two purposes; thermoregulation or camouflage.

By attempting to go back in time and determine conditions when the Map Butterfly evolved this trait of diphenism, a study by Fric et al.(see at end) argues that the timing of the two morphs makes no sense regarding thermoregulation (I’m not to sharp on phylogentics and cladistics so you’ll have to read that one for yourself if you want to know more, though I can see the point that having a dark morph in the summer WOULD seem kinda counterproductive).

As for camouflage, theories and plenty studies already exist on the effects of disruptive coloration on predator avoidance. The idea is that contrasted patterns break up the apparent outline of the butterfly making it more difficult for predators to spot. The general idea is that high contrast patterns work best, but mixed results have been reported in literature. Some studies came to show that too contrasty patterns made the prey more obvious to the predator.

Other than the colouring, there are several changes in body design between the two morphs of Map Butterfly (A. levana) that seem more obvious as to their purpose.
From orange (f.levana) to black (f.prorsa) there generally is a increase in size;

These morphological changes render the black summer generation more mobile and support theories of differential dispersal; one generation focused on mating and raising a large summer generation, that generation in turn more able dispersers, hopefully effectively colonizing new areas.

Two dark Map Butterflies ( Araschnia levana levana f. prorsa ). One looks like it was lucky to escape the grasp of a hungry predator.

More stuff to read:

• Map Butterfly at UKButterflies
• Hormonal control of seasonal morphs by the timing of ecdysteroid release in Araschnia levana L. (Nymphalidae: Lepidoptera) - P.B. Kocha and D. Bückmann
• Generations of the polyphenic butterfly Araschnia levana differ in body design - Fric, Z & Konvicka, M
• Red & black or black & white? Phylogeny of the Araschnia butterflies (Lepidoptera: Nymphalidae) and evolution of seasonal polyphenism - Fric et al.
• Seasonal polyphenism and developmental trade-offs between flight ability and egg laying in a pierid butterfly - Bengt Karlsson & Anna Johansson
• Enhancement of chromatic contrast increases predation risk for striped butterflies - Nina Stobbe & H. Martin Schaefer