Monday, 28 February 2011

Glasswing, the transparent butterfly

Image of the Glasswing Butterfly known for its transparent wings
Glasswing Butterfly
(Greta oto)
Kingdom: Animalia
Phylum: Arthropoda 
Class: Insecta
Order: Lepidoptera
Family: Nymphalidae
Genus: Greta
Species: Greta oto
Conservation Status: Not assessed
Common Name(s): Glasswing, Espejitos

While many butterflies are known for their bright colors and beautiful patterns, the glasswing butterfly is best known for being one of the few terrestrial animals that exhibit the strange trait of transparency.

As you can see on the image, these strange little critters have wings that are fully transparent, except for their brown borders, creating a window-like effect. In Spanish, the species is known as "espejitos", which roughly translates to "little mirrors".

There is not much research behind this unusual insect and thus we don't know much about it.

Habitat & Distribution
The species occurs in the rainforests of Central America, from Mexico to Panama, and Costa Rica, and as far south as Venezuela, in the mountain area that lies around the City of Caracas. 

Obviously, the most distinctive characteristic of the Greta Oto is its transparent wings. The opaque borders have a dark brown coloration. In some individuals, the borders are tinted with red or orange. The wings have a span ranging from 5.6 to 6.1 cm (~2.2 to 2.4 in). The body is dark colored.

Although seemingly fragile, the wings are quite robust, enabling the glasswing to go on long migratory flights, traveling up to 12 miles a day.

Glasswing Butterflies at London Zoo

Why are they transparent? What's the science behind it?
The glassy wings work as a means of camouflage, helping the butterfly to blend in with the environment, giving a hard time to predators detecting it.  In order for an animal to achieve true transparency, the tissues must first not absorb light. But this is not sufficient by itself. Neither can they scatter light. This means that the wings have the same refractive index all the way through them.

You can check the first reference, if you want to learn more about the structure of the wings.

More glasswing butterflies, from the London Zoo

Adults feed on the nectar of many common flowers, but seem to have a preference for the flowers of Lantana plants, a genus comprised of about 150 species of perennial flowering plants. 

Behavior & Reproduction
Interestingly, in order to find a mate, males congregate in the shady corners of the rainforest understory and then begin to excrete pheromones that attract females. Males are known to lek, meaning that they gather in large groups for the purpose of attracting females.

After mating has occurred, females lay their eggs on plants of the tropical Solanaceae genus, Cestrum.

The glasswing butterfly doesn't solely rely on camouflage. As aforementioned, females usually lay their eggs on Cestrum plants. Here is is where their second line of defense comes into play. 

The newly-born caterpillars, gorge themselves with these plants that contain certain toxic alkaloids. It is presumed that the caterpillars also become toxic by storing these compounds inside their tissues. As a result, most predators avoid the young larvae, due to their bad and possibly dangerous taste.

Adults also appear to be toxic, with their toxicity resulting from males feeding on certain flowers (e.g., species of the family Asteraceae), whose nectar contains pyrrolizidine alkaloids. The pheromones produced by males have also been found to contain the same compounds.  

Video showing a Glasswing Butterfly

Conservation Status
The conservation status of the glasswing butterfly has yes to be assessed. However, it is a relatively common sight and there has even been some success in breeding the species under captivity. Actually, in 2014 when I visited the london zoo, I was lucky enough to see many of them at the Butterfly Paradise. The first two videos in this post were shot by me.

It's safe to assume that the species is not under immediate threat.

A glasswing butterfly falls prey to a crab spider

References & Further Reading
- Binetti VR, Schiffman JD, Leaffer OD, Spanier JE, & Schauer CL (2009). The natural transparency and piezoelectric response of the Greta oto butterfly wing. Integrative biology : quantitative biosciences from nano to macro, 1 (4), 324-9 PMID: 20023733
- Hall, S. K. (1996). "Behaviour and natural history of Greta oto in captivity". Tropical Lepidoptera 7 (2).
- Lamas, G. (Ed.). (2004). Checklist: Part 4A. Hesperioidea - Papilionoidea. In: Heppner, J. B. (Ed.), Atlas of Neotropical Lepidoptera. Volume 5A. Gainesville, Association for Tropical Lepidoptera; Scientific Publishers.
- Brown, K. S. (1984). Adult obtained pyrrolizidine alkaloids defend ithomiine butterflies against a spider predator, Nature, 309: 707-709.

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