Scarlet Tiger Moth (Callimorpha dominula)

Scarlet Tiger Moth (Callimorpha dominula): A Concise Expert Guide

The Scarlet Tiger Moth (Callimorpha dominula) is one of Europe’s most recognisable day-flying moths, admired for its bold colouring and scientific importance. Found in damp habitats across the UK and beyond, it combines striking appearance with a fascinating evolutionary backstory.

Overview

Scientific name: Callimorpha dominula

Family: Erebidae (tiger moth group)

Flight period: May to July

Activity: Diurnal (active during the day)

Unlike most moths, it is frequently seen flying in sunshine, making it easier to spot than many nocturnal species.

Identification

The Scarlet Tiger Moth is visually distinctive and hard to confuse with other species:

Forewings: Dark with an iridescent green sheen and pale spots

Hindwings: Bright red with bold black markings

Wingspan: Around 4.5–5.5 cm

At rest, the moth conceals its red hindwings, revealing them only in flight—an effective anti-predator strategy.

Habitat and Distribution

This species prefers moist, sheltered environments, including:

• Riverbanks

• Marshes and wetlands

• Woodland edges

• Coastal valleys

In the UK, it is most frequently found in southern England and parts of Wales, though its presence is highly localised.

Across Europe, its range stretches from Scandinavia to the Mediterranean.

Lifecycle

The Scarlet Tiger Moth completes one generation per year:

Eggs: Laid on host plants in summer

Larvae: Hairy caterpillars feed on a variety of plants and overwinter partially grown

Pupae: Formed in spring within a cocoon near ground level

Adults: Emerge in late spring to early summer

The overwintering larval stage is a key survival adaptation in cooler climates.

Diet and Behaviour

Adults: Feed on nectar from flowers such as thistles and brambles

Caterpillars: Consume plants like comfrey, nettles, and dock

They are aposematic, meaning their bright colours signal to predators that they may be unpalatable. Birds quickly learn to avoid them.

Warning coloration (aposematism)

Its appearance isn’t just decorative:

• Dark forewings with white spots help camouflage it when resting

• Bright red/orange hindwings flash during flight

This is a classic example of Aposematism—a signal to predators that it may be toxic or unpalatable.

Lesser-Known Insights

Genetic Research Icon

The Scarlet Tiger Moth has been extensively studied in population genetics. Variations in its wing patterns helped scientists test theories of natural selection versus random genetic change. A population in Oxfordshire (Cothill Fen) has been studied for decades, making it one of the best-known moths in genetics research.

Unusual Colour Forms

Rare morphs exist with altered spot patterns or reduced markings. These variations are inherited and have been tracked over generations in wild populations. The most famous is the “medionigra” form (reduced black pigment). This has been studied extensively in evolutionary biology. In fact, it’s a classic example used in studies of natural selection.

Chemical Defence

Caterpillars can store toxins from their host plants, which persist into adulthood—reinforcing their warning colours. The caterpillars feed on plants that contain toxins (like comfrey and nettles), and they can retain some of these chemicals. This makes both caterpillars and adults far less appealing to predators.

Day-Flying Advantage

Flying in daylight allows them to exploit nectar sources with less competition from nocturnal moths.

Conservation Notes

While not globally threatened, the species depends heavily on stable wet habitats. Drainage, development, and habitat fragmentation can reduce local populations.

Encouraging native plants and preserving damp areas can help sustain colonies.

Here are five genuinely interesting facts about the Scarlet Tiger Moth:

1. It Helped Shape Modern Evolutionary Theory

This moth played a key role in 20th-century genetics debates. Long-term studies of its wing pattern variations were used to test how evolution works in real populations—whether driven more by natural selection or random genetic drift.

2. Some Populations Are Genetically “Famous”

A colony in Oxfordshire became one of the most intensively studied insect populations in the world. Scientists tracked individual moths over decades, making it a landmark case in population genetics research.

3. Its Bright Colours Are Backed by Chemistry

The red-and-black warning colours aren’t just for show. The moth can retain toxic compounds absorbed during its caterpillar stage, making it distasteful to predators even as an adult.

4. It Can “Flash” Its Colours to Startle Predators

When at rest, the moth hides its bright red hindwings. If disturbed, it suddenly reveals them in flight—this quick flash of colour can confuse or deter predators long enough to escape.

5. It Breaks the “Moth = Nocturnal” Rule

Unlike most moths, the Scarlet Tiger is comfortably active in daylight. This behaviour is relatively rare and is thought to work hand-in-hand with its warning colours, which are more effective when visible in bright light.

FAQs

Is the Scarlet Tiger Moth rare in the UK?

It is not rare overall but occurs in scattered, localised populations.

Why is it active during the day?

Daytime activity helps with feeding and may enhance the effectiveness of its warning colours.

What plants attract it?

Nectar-rich flowers for adults and leafy plants like comfrey for caterpillars.

Does it migrate?

No, it is a resident species and does not migrate.

Is it harmful to humans or gardens?

No. It poses no threat and is beneficial as part of a healthy ecosystem.

Final Thoughts

The Scarlet Tiger Moth stands out not just for its vivid appearance, but for its scientific relevance and ecological role.

Its presence signals a thriving habitat, and its study continues to inform our understanding of evolution and genetics.

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