Apatura ilia: The Fascinating World of the Lesser Purple Emperor
The Apatura ilia, commonly known as the lesser purple emperor, is a striking butterfly species that inhabits much of Europe and stretches across the Palearctic region. Named for its visual resemblance to the purple emperor butterfly, this member of the Nymphalidae family is celebrated for its iridescent beauty and complex biological variations.
From its mythological namesake—Ilia, the mother of Romulus and Remus in Roman mythology—to its presence on North Korean postage stamps, this butterfly holds a unique place in both natural history and cultural interest.
Key Facts
- Scientific Name: Apatura ilia (Denis & Schiffermüller, 1775)
- Wingspan: 55–60 mm in females; 60–70 mm in males
- Primary Habitat: Forests containing willow and poplar trees
- Flight Period: May to September
- Diet: Tree honeydew, moisture, and excrement
- Unique Ecology: The only studied European butterfly species whose northern range has moved slightly southward.
Physical Description and Identification
Identifying an Apatura ilia requires a keen eye for detail, as the species exhibits significant variation in color and pattern. The upper side of the wings is generally dark brown. In males, this base color is enhanced by shimmering metallic blue-violet hues. Both sexes feature a clear postdiscal band on the hind wing and several light spots on the fore wing.
Distinguishing Forms and Subspecies
One of the most notable aspects of this species is its distinct forms. The nominal form, ilia, features white markings, whereas the form clytie presents clear fawn or brownish markings. A key feature used to differentiate A. ilia from the similar Apatura iris is the presence of an orange-colored ocellus (an eye-like spot) on the fore wing.
The species also displays various regional subspecies and color variations, such as:
- A. i. lusitanica: A race found in Portugal with enlarged white eye-spots.
- A. i. eos Rossi: Found in Southern France and Northern Italy, characterized by a paler ground color and reduced violet gloss.
- A. i. serarum: A subspecies in West and Central China with dark ground color and white markings.
- A. i. metis: A form found in southern Russia where the eye-spots may disappear entirely.
Life Cycle and Biology
The life cycle of the lesser purple emperor is closely tied to its host plants. The caterpillar (larva) is typically 4–5 cm long, colored a dirty green. It features distinctive reddish horns on its head with a black stripe, and several red-margined yellow oblique stripes along its body. These larvae feed primarily on willows (Salix species) and poplars (Populus tremula and P. nigra).
After feeding, the caterpillar undergoes pupation. The chrysalis (pupa) is greenish, carinate (having a keel-like ridge) dorsally, and often hangs from a leaf or twig, mimicking the appearance of a young willow leaf. Depending on environmental conditions, the insect may pupate in the same year or overwinter as a young caterpillar.
Ecology and Distribution
While widely distributed across the Palearctic—reaching as far as Japan—Apatura ilia is notably absent from several regions, including the British Isles, the Nordic countries, and the Mediterranean islands. They are most commonly found in mountainous areas rather than plains.
Interestingly, ecological studies of 35 European butterfly species have identified A. ilia as an outlier. While most species show range shifts, A. ilia is the only one observed to have its northern limits move slightly southward while its southern limits remained stable.
| Feature | Details |
|---|---|
| Order | Lepidoptera |
| Family | Nymphalidae |
| Male Wingspan | 60–70 mm |
| Female Wingspan | 55–60 mm |
| Host Plants | Populus and Salix species |
| Primary Food | Tree honeydew |
Frequently Asked Questions
How can I tell the difference between Apatura ilia and Apatura iris?
The most reliable way to differentiate them is by looking for the orange-colored ocellus on the fore wing, which is present in A. ilia.
What do lesser purple emperor butterflies eat?
Adult butterflies primarily feed on tree honeydew and seek out moisture, honeydew shrubs, or excrement to sustain themselves.
Where is the best place to find this butterfly?
They are most abundant in mountainous regions across Europe and Asia, specifically in habitats where willow and poplar trees are prevalent.
What are the main host plants for the caterpillars?
The larvae feed almost exclusively on various species of willow (Salix) and poplar (Populus), such as Populus tremula and Populus nigra.
Is the butterfly's color permanent?
The color can vary significantly between individuals and forms. For example, males often show a metallic blue-violet gloss, but some forms or subspecies may appear much darker or even lack the gloss entirely.