One Butterfly, Two Faces: The Map Butterfly (Araschnia levana) in the Wildlife Garden

Summary

• The Map butterfly (Araschnia levana) is a native butterfly that displays two completely different colour morphs across the seasons (seasonal dimorphism).
• The spring generation (levana) features a vibrant orange-brown pattern, whereas the summer generation (prorsa) appears almost black with a striking white band.
• This transformation is not caused by altered genetics, but by the day length (photoperiod) experienced by the caterpillar during its development.
• Both generations bear a delicate network of lines on the underside of their wings that resembles an antique map—the feature that gives the species its common name.
• In a wildlife-friendly garden, you can actively support this species by preserving unmown patches of nettles in damp, sheltered margins and leaving standing plant stems for overwintering pupae.

Two Butterflies or One? The Mystery of the Wing Pattern

Imagine walking through your garden in May and spotting a delicate butterfly with a bright orange-red ground colour and fine black spots fluttering along a flowering woodland edge. A few weeks later, at the height of summer, you see a butterfly of the exact same size in the very same spot, yet the upper surface of its wings is deep velvety black, crossed by a broad white band.

At first glance, one might easily assume they are two entirely distinct species. In reality, this observation represents one of the most fascinating phenomena in the native insect world: both butterflies belong to the very same species, the Map butterfly (Araschnia levana).

In biology, this phenomenon is known as seasonal dimorphism or seasonal polyphenism. As highlighted by the thematic outline in the YouTube description, the Map butterfly is a classic textbook example of environmentally cued developmental biology: the genetic makeup of both generations is identical, yet the environment dictates which guise the butterfly assumes.

A Profile of the Two Generations

To reliably identify both forms in the garden, it helps to take a closer look at the characteristics of each generation.

1. The Spring Form: Araschnia levana f. levana

The adults of the first generation emerge from pupae that have overwintered. Depending on the weather and region, they fly from April to June.

• Upperside: A warm, yellowish-orange to foxy-red ground colour patterned with a network of black spots and markings. Superficially, it resembles smaller fritillaries or tortoiseshells.
• Behaviour: The butterflies capitalise on the first warm days of spring to take nectar from early-flowering shrubs and herbaceous plants along woodland rides, clearings, and shrub borders.

2. The Summer Form: Araschnia levana f. prorsa

Caterpillars hatch and grow in early summer from eggs laid by the spring generation. The adults of this subsequent brood fly in July and August.

• Upperside: A dark brown to almost velvety black ground colour, marked with an interrupted, whitish to cream-coloured transverse band and delicate rust-coloured marginal lines.
• Behaviour: These butterflies are highly active in midsummer, frequently visiting flowering perennials such as hemp-agrimony or wild brambles.

The Connecting Clue on the Underside

Although the uppersides of the two forms bear virtually no resemblance to each other, the wing undersides reveal their shared identity. Both generations display an intricate pattern of reddish-brown, ochre, and whitish patches traversed by a fine web of pale veins. This design bears a striking resemblance to the road and boundary network on an antique cartographic map—hence the species' common name.

What Drives the Colour Shift? Control by Light

For a long time, it remained unclear how two such contrasting morphs could arise from identical genetic material. Today, the biochemical and ecological mechanisms are well understood:

1. The Photoperiod as a Cue: The decisive factor is the day length perceived by the caterpillar during its larval development. Caterpillars that grow in spring under the lengthening days of early summer (long-day conditions) receive the signal to develop directly without entering a winter dormancy.
2. Hormonal Signalling: Through the caterpillar's nervous system, day length regulates the release of specific hormones (notably ecdysone during the pupal phase). This hormonal pulse determines which pigments (melanins for dark tones, or pterins and ommatins for reddish-orange hues) are deposited into the developing wing scales.
3. Short Days and Winter Diapause: The caterpillars of the summer generation develop in late summer as day length wanes (short-day conditions). This signal instructs the pupa to enter a state of developmental arrest (diapause) and overwinter. The following spring, the orange levana form emerges once again.

Direct Comparison of the Generations

Practical Guide: Transforming Your Garden into a Map Butterfly Habitat

Observing both generations of the Map butterfly in your garden requires structurally diverse habitats. As an inhabitant of woodland edges, clearings, and damp margins, the species relies on an interplay of specific larval host plants, sheltered pupation sites, and sunny nectar sources.

   [ Shrub edge / Semi-shade ]         -->   Shelter & microclimate
                 │
   [ Nettle patches (damp) ]           -->   Egg-laying & larval food plant
                 │
   [ Unmown tall-herb fringes / Litter]-->   Pupal overwintering
                 │
   [ Nectar-rich perennial borders ]   -->   Nectar for both adult forms

Step 1: Cultivating the Right Nettle Corner

The caterpillar of the Map butterfly specialises on the stinging nettle (Urtica dioica). However, the species generally avoids isolated, dry, hot nettle stands in full sun:

• Selecting the location: Position or retain nettle stands in semi-shaded, sheltered spots with slightly moist soil—such as the base of a native hedge or behind a compost heap.
• Patch size: A few solitary stems are rarely sufficient. Aim for a dense clump of at least one to two square metres, where the microclimate remains stable even during hot summer spells.

Step 2: Providing Undisturbed Overwintering Sites

The chrysalis of the Map butterfly is a succumbent pupa: it anchors itself head-downwards to plant stems, twigs, or dry leaf litter close to the ground using a silk pad.

• Avoid autumn clearance: Do not cut back borders and perennial fringes right down to the ground ahead of winter. Retaining old stems and a natural leaf litter layer provides essential protection for resting pupae.
• Rotational management: When undertaking maintenance, prune in sections so that untouched refuges always remain.

Step 3: Planting a Continuous Nectar Corridor

Because the two adult morphs fly at different times of the year, they require a staggered succession of nectar from native wild plants:

• For the spring generation (April–June):
  • Spring-flowering woody plants such as goat willow (Salix caprea), blackthorn (Prunus spinosa), or hawthorn (Crataegus).
  • Herbaceous margin plants such as ground ivy (Glechoma hederacea), garlic mustard (Alliaria petiolata), or wood forget-me-not (Myosotis sylvatica).
• For the summer generation (July–August):
  • Umbellifers and composites in sunny locations, notably hemp-agrimony (Eupatorium cannabinum), purple loosestrife (Lythrum salicaria), wild bramble (Rubus fruticosus), or brown knapweed (Centaurea jacea).

Limitations and Frequently Asked Questions (FAQ)

Can the Map butterfly be confused with other species?

Yes, particularly because of its two distinct morphs:

• Spring form (levana): At a glance, it may be mistaken for the small tortoiseshell (Aglais urticae), though the latter is considerably larger and more boldly marked. Various fritillaries (such as Melitaea species) also share similar colouration, but lack the distinctive cartographic web on the wing underside.
• Summer form (prorsa): From a distance, it resembles the white admiral (Limenitis camilla). However, the Map butterfly is far smaller (wingspan typically only 30–35 mm) and reveals its brown-and-white veined network beneath.

Does a third generation occur in a single year?

In exceptionally warm years and climatically favoured regions, a partial third generation may emerge in late summer or early autumn. These individuals generally resemble the summer form, though intermediate markings can occur. However, the majority of offspring reliably enter pupal diapause as day lengths decrease.

Why do Map butterflies avoid the nettles in my sunny borders?

Butterfly larvae often have very precise microclimatic requirements. Araschnia levana prefers shaded to semi-shaded borders with higher relative humidity. Fully exposed nettle stands in direct sun are far more likely to be colonised by the peacock (Aglais io) or small tortoiseshell (Aglais urticae).

Do insect hotels benefit the Map butterfly?

No. Conventional nest boxes and bug hotels made of drilled wood or reeds cater to cavity-nesting solitary bees and wasps. Butterflies like the Map butterfly depend on healthy vegetation structures, larval food plants, and undisturbed herbaceous margins for pupation.

Sources and Further Information

• Video Reference: Overview of seasonal dimorphism in the Map butterfly from the thematic outline in the YouTube description.
• Garden Ecology Resource: For details on the value of natural margin structures and food plants, visit Naturkompass Gartenexpedition.
• Note on additional links: Commercial links (online shops) and inaccessible social media channels referenced in the original video description have been omitted in accordance with source quality standards.