Wednesday, 20 July 2011

The Incredible Glasswing Butterfly

A butterfly with transparent wings? Surely not. Yet there is a species that exhibits this trait. Take a close look at the incredible Glasswing, an enchanting species that confounds science.

Greta oto may sound like the name of a silent movie star from Eastern Europe but is in fact the scientific name for one of the most exquisite – and little known – species of butterfly on the planer. This butterfly’s claim to fame is that its wings, spanning up to six centimeters, are almost completely transparent. That’s right, you can see just about right through them.

The common English name for this remarkable butterfly is glasswing, which in itself speaks volumes about the appearance of this small but unusual insect. However, it takes the romance languages to step in and give the butterfly the name which, for many, suits it best. The Spanish name for the glasswing is ‘espejitos’. Literally translated, this means little mirrors. Just a glance at the insect in question and one can imagine the thrill of pleasure when the moment of inspiration that came to its Hispanic name giver.

A close look at Greta oto reveals that between the veins of its wings the tissue is virtually see through) or, properly, translucent). Most other butterflies have colored scales which pattern the wings, quite often to ward off predators. The glasswing has another way of doing this entirely, but over the millennia it has evolved these specific wings to hide itself from predators rather than to warn them off. The only way that you can tell that it has wings at all are the borders, which are of a dark hue, sometimes bordering on the orange. Were it not for these borders, the glasswing would be more or less invisible to the human eye.

The glasswing is part of a specific clade of butterfly. Now for the science, as Jennifer Aniston used to say. A clade is a ‘branch’ and is a term used in the taxonomy of species. When groups of species has a single common ancestor (which does not necessarily need to be extant) then it is known as monophyletic. The common ancestor of the glasswing is long extinct but the clade it belongs to is known as the clearwing clade.

Transparency in nature is not something that has been very well understood. In order to achieve transparency the tissue must not absorb light. Neither can it scatter light, as this is the major obstacle to being see-through. Humans, for example, will never be able to be transparent because they have chemical and biological compounds that all have different refraction.

The wings of the glasswing must, therefore, have the same refractive index all the way through them as otherwise this transparency could not possibly occur. It is thought (a postulation at the moment rather than sure fire fact) that the surface of the wing has a covering of protrusions that are so small they can be called submicroscopic. They have a single refractive index and so do not scatter light, so making the wings transparent.

As with most butterflies it is a delicate looking species, but those who breed it in captivity have found it to be quite resilient and its wings are no less strong than those of other species. Another relief is the fact that in its native habitat it is quite common. Unless you live in South America, however, the only chance you will get of seeing the glasswing alive is in a butterfly house or farm.

If you want to see ‘little mirrors’ in the wild, however, you will have to take a trip – anywhere from Mexico to Panama in Central America will do the trick. You will also have to locate the nearest rainforest as the understory of this environment is where the glasswing prospers. They feed off the nectar of a variety of rainforest flowers but when it comes to laying their eggs and ensuring the survival of the next generation, the glasswing has a fine trick up its (metaphorical) sleeve.

The glasswing, where possible, will lay its eggs on a plant of the genus ‘Cestrum’. Its common name, to you and I, is the nightshade and it is highly poisonous. The caterpillars, which are striped in bright purple and red to warn possible predators, are thus a snack that birds and other animals will not enjoy at all. The alkaloids, a chemical in the plants that occurs naturally and is full of nitrogen, stay in the bodies of the glasswing in to adulthood meaning that even then they will not be an attractive meal.

During mating, which can last for many hours, usually starting in the early afternoon, the males will convert some of these alkaloids in to pheromones which will attract the females to them. The glasswing is also noted for its long migrations and the fact that the males of the species, when about to meet, practice lekking. This is when a host of males gather together to show off their best features en masse – the females then choosing the most dominant and visually exciting.

The glasswing, while not rare as a species, is one of very few land based animals that have successfully mastered the act of transparency. Now you see it, now you don’t.



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