The Common Mormon Butterfly Explained

The common mormon (Papilio polytes) is a large black swallowtail butterfly of India and South-East Asia, best known because its females occur in several forms, two of which imitate the poisonous common rose and crimson rose butterflies to avoid being eaten by predators. The common mormon is a regular visitor to gardens, parks and forest edges across India, and it breeds on citrus and curry leaf plants.

Males are plain and consistent, but females are variable, and this difference makes the common mormon one of the best-studied examples of mimicry in the world. This explainer covers how to identify the species, how the female forms work, which plants the caterpillars eat, and how to attract the butterfly to a garden.

Key Takeaways

• The common mormon (Papilio polytes) is a large swallowtail butterfly with a black body and wings that is common across India.
• Male common mormons are black with a band of white patches across the hindwings, and they have only one form.
• Female common mormons occur in three forms: cyrus, which resembles the male, and stichius and romulus, which mimic poisonous rose butterflies.
• Mimicry in the common mormon is Batesian mimicry, in which a harmless species imitates a distasteful one to deter predators.
• The common mormon caterpillar feeds on plants of the citrus family, including lemon, lime, orange and curry leaf.
• Research led by Indian scientists and colleagues showed that a single gene, doublesex, controls the choice between the female forms.

What Is the Common Mormon Butterfly?

The common mormon is a medium-to-large swallowtail butterfly, scientifically named Papilio polytes, that is widespread across tropical Asia and is one of the most familiar butterflies in Indian gardens. It belongs to the family Papilionidae, the swallowtails, which includes the birdwings, the lime butterfly and the blue mormon.

Unlike many swallowtails, the common mormon has no long tail projecting from each hindwing. Instead, the hindwing has a gentle scalloped edge with a small, blunt tail-like projection. Its flight is strong and direct but often fluttering when it visits flowers.

The Indian population is called the subspecies romulus, which is also the name given to one of its female forms. That overlap sometimes confuses new butterfly watchers, who should remember that “romulus” can refer to either a subspecies or a female form, depending on context. The origin of the common name “mormon” is uncertain. A popular explanation is that early naturalists compared the species’ many female forms to a household with many wives, though this is only a traditional account.

How Do You Identify a Common Mormon?

You can identify a common mormon by its overall black colouring with a row of white or cream patches across the hindwings in males, while females are recognised by their forms. Size and flight help too, since it is noticeably larger than most whites, yellows and blues.

The Male

The male has velvet-black wings. On the hindwing, a band of elongated white patches forms a curved stripe. The forewings have faint pale streaks along the veins. The body is black. Males are often seen sipping minerals from damp soil, a behaviour known as mud-puddling, sometimes in groups.

The Female

The female is much more varied, as the next section explains. All female forms are somewhat broader-winged than the male. Look for the pattern of white patches and red spots, as these identify the form.

Similar Species

• Blue mormon (Papilio polymnestor): Larger, with a bluish sheen and a soft blue patch across the hindwings.
• Common rose (Pachliopta aristolochiae): Black with a red body and a white patch on the hindwing; it is the model that the stichius form copies.
• Red helen (Papilio helenus): Black with a prominent white patch on the hindwing, found mainly in hills and forest.

Why Do Female Common Mormons Look Different?

Female common mormons look different because the species shows female-limited polymorphism, meaning that only females appear in several forms, and two of those forms evolved to resemble poisonous butterflies. Males show no such variation.

The pattern of such variation has fascinated naturalists since the 19th century. Alfred Russel Wallace studied female-limited mimicry in swallowtails in the 1860s, and it became an important example in debates about natural selection. In the common mormon, the non-mimetic cyrus form is not a rarity, and its frequency varies from region to region.

How Does Mimicry Protect the Common Mormon?

Mimicry protects the common mormon because predators that have learned to avoid the bitter-tasting rose butterflies also avoid the harmless female mormons that look like them. This strategy is called Batesian mimicry, named after the English naturalist Henry Walter Bates, who described it in 1862 after studying butterflies in the Amazon.

The model species, the common rose and the crimson rose, feed as caterpillars on Aristolochia plants (birthwort), which contain toxic aristolochic acids. The butterflies keep these chemicals in their bodies and are therefore distasteful or harmful to birds, lizards and other predators. Their bright red and black pattern is a warning signal.

The common mormon caterpillar eats citrus leaves, not Aristolochia, so the adult butterfly carries no such toxins. The female forms stichius and romulus gain the benefit of the warning pattern without paying the chemical cost. For the system to work, the mimic must be less common than the model, otherwise predators would have too many harmless experiences with the pattern and stop avoiding it.

What Genetic Switch Controls the Mormon’s Female Forms?

A single gene called doublesex controls the female forms of the common mormon, acting as a “supergene” that selects whether a female looks like a male or like a mimic. Doublesex is a well-known gene that helps determine sexual characteristics in insects, and in this species it has been adapted to control wing patterns as well.

A 2014 study published in the journal Nature, led by Krushnamegh Kunte of the National Centre for Biological Sciences in Bengaluru with colleagues, showed that the mimicry alleles lie in a region that includes doublesex. Females carrying the mimetic version of the gene develop the pattern of red spots and reduced white patches. The mimetic form is dominant over the non-mimetic one, so only one copy is needed to produce a mimic.

The discovery was significant because it explained how a complex set of traits can be inherited together as a single unit. It also showed how a gene that controls sex-specific development can be reused to create sex-limited colour patterns. The work made the common mormon a model organism for studies of adaptation, and it helped explain why only the females carry the mimetic patterns.

What Plants Does the Common Mormon Caterpillar Eat?

The common mormon caterpillar eats leaves of plants in the citrus family, Rutaceae, including lemon, lime, orange, pomelo, curry leaf and wood apple. This makes the butterfly a familiar visitor to backyard gardens and orchards.

Common Host Plants in India

• Citrus species: Lemon, sweet lime, orange and pomelo.
• Curry leaf (Murraya koenigii): A very common host in home gardens.
• Bael and wood apple: Aegle marmelos (bael) and Limonia acidissima (wood apple).
• Wild Rutaceae: Such as Glycosmis pentaphylla, Zanthoxylum and Toddalia.

Female butterflies lay single round eggs on young, tender leaves. They prefer fresh flush growth, so a plant that has recently been pruned is often chosen. Although the caterpillars eat citrus leaves, they rarely cause serious damage to mature trees. They can, however, slow the growth of small saplings and nursery plants, where gardeners sometimes remove them by hand.

What Is the Life Cycle of the Common Mormon?

The common mormon has a complete life cycle of four stages, egg, caterpillar, pupa and adult, which together typically take about a month in warm weather. In tropical India, the butterfly may breed through most of the year, with peaks after the monsoon.

1. Egg: A small, round, pale-yellow egg is laid on a tender leaf. It darkens before hatching in a few days.
2. Caterpillar: The young caterpillar is brown and white, resembling a bird dropping. As it grows, it moults several times (instars) and becomes green with a pale diagonal band across the body in the final stage.
3. Pupa: The caterpillar attaches itself upright to a twig with a silk girdle and forms a chrysalis that can be green or brown, matching its surroundings.
4. Adult: The butterfly emerges after one to two weeks, dries its wings and starts feeding on nectar.

The caterpillar has an additional defence: if disturbed, it extends a forked, orange-red organ behind its head called the osmeterium, which releases a strong-smelling chemical to ward off small predators such as ants and wasps.

How Can You Attract Common Mormons to a Garden?

You can attract common mormons to a garden by growing both nectar flowers for adults and citrus-family host plants for caterpillars, while avoiding pesticides. A butterfly garden requires both food sources, because adult butterflies lay eggs only where suitable leaves are available.

Host Plants

Plant a lemon tree, a curry leaf shrub or a potted lime. Leave some leaves for caterpillars, even if they look chewed. A single plant can support several caterpillars without much damage.

Nectar Plants

Adult mormons favour bright, tubular or clustered flowers such as ixora, lantana, zinnia, marigold, pentas and jasmine. They typically flutter their wings rapidly while feeding rather than settling completely.

Garden Practices

• Avoid chemical pesticides, which kill caterpillars and adults.
• Provide a shallow dish of damp sand or soil for mud-puddling males.
• Offer partial shade and shelter from strong wind.
• Keep native shrubs and some untidy corners to provide roosting places.

Is the Common Mormon Threatened?

The common mormon is not threatened, as it is a widespread and abundant butterfly that adapts well to gardens, farmland and towns. Its ability to feed on cultivated citrus and curry leaf plants helps it thrive in human-modified landscapes.

That said, butterflies in general face pressures from habitat loss, heavy pesticide use and climate change. Local numbers can fall where gardens are replaced by concrete and where sprays are used heavily. In India, wild animals are protected under the Wildlife (Protection) Act, 1972, and collecting or trading in butterflies can be restricted, so enthusiasts are encouraged to observe and photograph rather than collect.

Citizen science projects, such as India Biodiversity Portal and iNaturalist observations, now collect sightings of the common mormon. These records help researchers track the seasonal pattern and distribution of its different female forms across the country.

Bottom Line

The common mormon is a common butterfly with an uncommon story. Its males are plain, but its females carry a genetic switch that lets them choose between looking like a male or disguising themselves as poisonous roses. Growing a lemon tree or curry leaf plant is often all it takes to bring this living textbook example of mimicry into an Indian garden.

Frequently Asked Questions

What is the scientific name of the common mormon butterfly?

The scientific name of the common mormon is Papilio polytes. It is a member of the swallowtail family, Papilionidae. The subspecies found in India is called romulus.

Why is the common mormon called a mimic?

The common mormon is called a mimic because some females look like the poisonous common rose and crimson rose butterflies. Predators avoid the toxic roses, and so they also tend to avoid the look-alike female mormons. This is called Batesian mimicry.

Are common mormon butterflies poisonous?

No, common mormon butterflies are not poisonous. Their caterpillars feed on harmless citrus-family plants and do not store toxins. Only their look-alike patterns suggest danger to predators.

What do common mormon caterpillars eat?

Common mormon caterpillars eat the leaves of plants in the citrus family, such as lemon, lime, orange and curry leaf. They also feed on wild relatives such as Glycosmis and wood apple. Young caterpillars prefer tender new leaves.

How long does a common mormon live?

An adult common mormon usually lives for a few weeks, while the full life cycle from egg to adult takes about a month. Exact timing depends on temperature and food. Adults may live longer in cool, sheltered conditions.

Where is the common mormon found in India?

The common mormon is found across most of India, in plains, hills and urban areas. It is particularly common in peninsular India, the Western Ghats, the Gangetic plains and the foothills of the Himalayas. It is less common in very dry deserts and at high altitudes.

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