Glasswing butterflies have transparent wings that allow them to fade into a green and gloomy mosaic of leaves. The Florida Museum of Natural History has a credit.
With over a million known species, insects are the most diverse group of organisms on Earth, with conservative estimates indicating there are millions more waiting to be found. The rate of discovery may be outpaced by extinction due to human pressures.
Scientists must first know where the species are. The distribution of some plant and animal groups have been mapped, but little is known about the location of the world's insects.
Researchers created the most detailed distribution map to date of butterflies in the American tropics, showing that areas of highest diversity coincide with regions most threatened by development. The study focused on Ithomiini, a large group of glasswing butterflies, which occur throughout much of Central and South America. They may be a good indicator of the fate of other insects in the region.
One approach to understanding the diversity of insects is to focus on groups that reflect the diversity of all insects and for which we have good knowledge, like butterflies.
Credit: Doré et al.
Both help and hinder glasswings.
Glasswing butterflies have transparent wings marked with colorful spots of alternating colors. These markings are a warning for the butterfly species. Male glasswing butterflies feed on the poisonous plants and then pass the toxins to females when they are ready to mate. The butterflies and their eggs have a bitter taste because of the toxins.
The would-be predator isn't born with innate knowledge of not eating these butterflies, instead learning through trial and error. Many glasswing species have evolved wing patterns that give them strength in numbers.
The cost of educating predators to avoid them is shared by different species since they share the same warning color patterns.
The Mllerian mimicry has helped glasswing butterflies survive in the tropics, but it also comes at a cost. The extinction of any one species could jeopardize the survival of others, as this strategy is effective when all species are thriving. If one of the more common species goes extinct, all the others lose out on the benefit of being involved in Mllerian mimicry with those butterflies.
The transparent tendencies of butterfly counterparts are also shared by glasswing caterpillar and their chrysalide. Credit: André Freitas.
Glasswing butterflies are vulnerable at high altitudes.
Willmott and his colleagues have spent the last several decades trekking across mountains and forests in search of glasswings, describing new species and documenting their natural history along the way. The researchers combined the data they've collected over the years with information from more than 60 museums and private collections. They used the data to map the diversity of glasswings and the interactions between them in the American tropics.
Glasswings are very diverse in the Amazon River basin, where their transparent wings help them blend in against the forest gloom. Most of the species cluster together. The eastern slopes of the Andes Mountains contained the top 5% of glasswing diversity.
Glasswing diversity in the tropics often overlaps with areas at the highest risk of habitat loss due to land conversion for agriculture. This was true for species with restricted distributions, showing the need for efforts to conserve them.
Mountainous regions create a variety of environments when they climb. A large number of species can be found in the young Andes, which are among the world's highest mountains. The Andes is an ideal place to grow a variety of crops because of its different climates. "Loss of habitat is the most significant threat at the moment," Willmott said. It is unfortunate that areas that are good for people to live are also areas that support high animal and plant diversity.
Habitat destruction can be problematic for glasswing butterflies and caterpillar, which rely on a particular suite of plants for food and protective toxic compounds. Credit: Keith Willmott.
Mal Doré, a PhD student at the National Museum of Natural History in Paris, is worried that climate change may limit the range of already restricted species on the slopes of tropical mountains. As temperatures increase, species may be able to shift their distributions to higher altitudes, but whether glasswing communities will be able to keep up with climate change is not certain.
The lower and older mountains along the Brazilian Atlantic coast are home to a number of rare and endemic glasswing species, which face threats from habitat destruction. The region has experienced almost five centuries of human occupation, but it was also here that the first initiatives to protect Neotropical butterflies and their habitats were born.
Willmott and his colleagues are still optimistic. A detailed map of where butterflies occur can be used to protect environments and communities that are under threat.
"With more accurate maps of butterfly distributions, we can identify species and communities that currently lack protection, to more effectively focus limited resources where they are most needed."
Anthropogenic pressures coincide with Neotropical biodiversity hotspots in a flagship butterfly group. The DOI is 10.1111/ddi. 13455.
The journal contains information on diversity and distribution.
A map of transparent butterflies highlights a biodiversity hot spot in the Andes Mountains.
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