The Madagascan Sunset Moth: A Noble Spirit of Madagascar

Written and verified by biochemistry Luz Eduviges Thomas-Romero

Last update: 22 December, 2022

The Madagascan sunset moth (Chrysiridia rhipheus) belongs to the order Lepidoptera and the family Uraniidae. This species has a very distinctive feature that’s attracted the attention of people in the region for years: Its strong iridescence.

The pattern of the wings of this daytime moth is quite unusual, as it has several metallic colors on its wings and the iridescence exists even in the ventral area. If you want to know more about this fascinating flying invertebrate, we invite you to keep reading.

The Madagascan sunset moth is a member of a large family

In general, insects of the Lepidoptera order – which include butterflies and moths – are the second most important pollinators on the planet. They have in common the fact that they develop through four stages of life.

Thus, they undergo metamorphosis and feed on their own eggshells for their first meal. There’s a great variety of Lepidoptera all over the world, with 20,000 different species and an unusual diversity of shapes and colors. The size of these insects can vary from 1/8 inch to 12 inches.

In addition, Lepidoptera share many aspects with one other, such as the ability to see only 3 different colors: red, green, and yellow. However, there are still enough morphological and physiological differences to distinguish the different taxa within this order.

A special animal because of its iridescence

It’s interesting to know that the amazing appearance of this beautiful moth is due to its iridescence. That is, the optical phenomenon that’s generated when its wings reflect light.

Light reflects off its wings forming an arc, in such a way that it exhibits bands of the 7 essential colors. Thus, its wing surface shows different shades of light according to the angle of observation.

In this type of coloring, there’s no pigment. In this sense, its tone has to do with the structure or arrangement of very small scales, which vary in size and shape. For this reason, we know this phenomenon as structural coloration.

The distribution of pigments with different colors usually produces the color patterns on the bodies of animals. However, other animals, such as the Madagascan sunset moth, use the spatial variation of color-producing microstructures.

The coloration of the Madagascan sunset moth is the subject of study

Scientists are studying the structural coloration of the sunset moth. Its wings have a periodic microstructure in sub-micron size, which produces its wonderful brightness. The morphology of its scales and the spatial variation of the microstructure are an interesting example of physical phenomena, such as optical interference and diffraction.

Distribution and diet

The sunset moth is an endemic insect of Madagascar. This is mainly due to its strong association with plants of the genus Omphalea, which thrive on the island.

In its caterpillar stage, it’s defined as a specialist. That’s because the larvae feed exclusively on plants of the genus Omphalea, specifically on the species ankaranensis, palmata, occidentalis, and oppositifolia. However, the adult sunset moth is a generalist, as it feeds on the nectar of a wide variety of plants.

Although the adult moth no longer depends on Omphalea plants, it never strays too far from them. This is due to the plant’s need for its larva to survive. Adults have daytime habits and only lay their eggs on the underside of the leaves of Omphalea plants.

A final secret weapon

Once the eggs hatch and the larvae emerge, the caterpillars feed on the Omphalea plant. The intake has two purposes: nutrition and chemical defense. This plant species produces a powerful toxin. And, once the larva ingests it, will remain with the insect for the rest of its life.

It’s interesting to know that the caterpillar consumes the plant and almost instantly uses the toxins to defend itself from potentially pathogenic ants, which also reside on the plant itself.

These ants, which generally attack the insects that try to feed on the plant, ignore the larva that excretes the toxin. Later, when it reaches the adult stage, the sunset moth and its pupa no longer excrete toxins. However, they store them to deter their predators.