A striking double-eyed owl butterfly has emerged at the Natural History Museum's Sensational Butterflies exhibition.
Close-up of the unusual double-eye pattern on the owl butterfly.
Owl butterflies usually have a single 'owl eye' pattern called ocelli on each of their hind wings. But last weekend one emerged from a chrysalis with a double-eyed pattern.
It was spotted by Luke Brown, Sensational Butterflies butterfly house manager. 'In more than 30 years of working in butterfly houses, I must have seen over a million butterflies emerge from their chrysalises, and I have never seen one like this,' he says.
Butterfly expert at the Museum, Blanca Huertas, searched the around 3,000 specimens of owl butterflies (those in the Caligo genus). She says, 'Despite checking our collection, one of the largest in the world and our famous collection of aberrations, we could not find a similar specimen.'
The Caligo or owl butterflies belong to the Nymphalidae family and include some of the largest butterflies of the neotropics. Their distinctive eye patterns have been shown in studies to be effective in deterring predators such as birds. Their large size makes them popular in butterfly houses.
They lay eggs in clusters, usually in banana plants where they can become pests, causing severe damage to plantations. Adults feed on rotting fruits and sap.
The usual owl butterflies have a single 'eye' or ocelli on their hind wing.
This rare double-eyed butterfly is the species Caligo eurilochus.
Its pupa was imported from Costa Rica for the Sensational Butterflies exhibition, where visitors can see hundreds of live butterflies from all over the world in all stages of a butterfly's life cycle.
The double-eye may be due to a rare event during the larval development of this individual, says Blanca. The pattern development of wings occurs in a two-step process during the larval stages and during the first days of adult development. 'The development of the ocelli is a complex process and this is a clear case of an unusual genetic variation of a condition not often seen, known as an aberration,' says Blanca.
Like most butterflies, this species of owl butterfly has a short lifespan. This one lived for only a few days and it seemed to have a problem with its wings.
Normally, when a butterfly emerges from its chrysalis, fluid from its body is sent into veins in the wings to pump them up and dry them out. The fluid then drains out from the butterfly's body. Usually a butterfly is ready to fly in about 3 hours. However, Luke noticed that this individual couldn't drain its wing veins of the fluid. 'It meant the wings would have been too heavy for the butterfly to fly,' he adds.
The Museum looks after a collection of around 4.5 million butterflies. 'The specimen is now kept safe in the collections where researchers can study more about this unusual variation. And it is in good condition thanks to the prompt action of Luke,' says Blanca.
There are about 20,000 species of butterfly worldwide and more than 6 times as many species of moth. An amazing 40% of these are found in South America. However, there are many more species still undiscovered or not scientifically named yet.
The most reliable way to tell butterflies from moths is to look at their antennae. Butterfly antennae have a clubbed tip whereas moth antennae are usually thread-like or feathered.