Panama has some insects that look as though someone has taken a perfectly ordinary beetle, dipped it in molten gold and then polished it until it shines. Among the most spectacular are the jewel scarabs of the genus Chrysina, a group of scarab beetles famous for their metallic green, gold, bronze and silver bodies. They are not simply colourful insects. Their extraordinary appearance comes from microscopic structures in their exoskeletons that manipulate light, making them a fascinating example of natural optical engineering. Panama is particularly interesting for these beetles because modern taxonomic work has revealed an unexpectedly rich diversity of Chrysina species in the country.
Panama is a hotspot for jewel scarabs
A major scientific revision published by Manuel Barria of the University of Panama examined the genus Chrysina in Panama, Colombia and Ecuador. The study recognized 28 species across those three countries, with 25 occurring in Panama. Even more interestingly, three species were recorded from Panama for the first time in that work. Several other species were found in new locations, and Chrysina aurora was rediscovered in Veraguas after an extraordinary 147 years since the species had originally been described from a female specimen.
That tells us something important about tropical insects. You can have an insect that has technically been known to science for more than a century and still have surprisingly little information about where it lives, how common it is or how variable it can be. Panama's mountains, cloud forests, lowland rainforest and isolated valleys create an enormous number of ecological opportunities for insects to specialize.
And Chrysina is only one part of the enormous scarab family. A comprehensive study of dynastine scarabs in Costa Rica and Panama, for example, documented 157 species in that particular group alone.
The gold is not actually gold
One of the coolest scientific facts about these beetles is that their metallic appearance isn't produced in the same way that a gold object shines.
The spectacular colours of Chrysina come from the microscopic physical structure of the beetle's exoskeleton. In other words, the beetle is using nanostructure rather than pigment to produce much of its metallic appearance. Research on the golden jewel scarab Chrysina resplendens has shown that its exoskeleton contains intricate nanoscale structures responsible for its metallic sheen.
This is an example of structural colouration. Instead of simply containing a chemical pigment that absorbs some wavelengths of light and reflects others, microscopic structures interact with incoming light. The result can be an intense metallic appearance that seems almost artificial.
That is why a golden scarab can look less like an animal and more like a piece of jewellery.
Nature has effectively built a microscopic optical device onto the outside of the beetle.
Why does a beetle need to look like this?
This is where things become more complicated.
It is tempting to assume that the brilliant metallic colour must have evolved for one obvious reason, such as attracting a mate or frightening predators. But colour in insects can have several functions, and researchers cannot automatically assume that one spectacular explanation is correct.
Metallic surfaces can affect how an animal is seen under different lighting conditions. In a rainforest, sunlight is constantly changing as it passes through leaves, branches and gaps in the canopy. A beetle sitting on vegetation can therefore look dramatically different depending on the angle of the sun and the observer.
The physics of structural colour is also extremely interesting because the apparent colour can depend on the geometry of the microscopic structures and the direction from which light reaches them.
So when you see a golden beetle in Panama suddenly flash like a tiny piece of jewellery, you are looking at a very sophisticated interaction between light, nanostructure and biology.
Some Panama jewel scarabs are not simply gold
Another fascinating feature of Chrysina is that the genus isn't limited to one particular colour.
Panamanian species include beetles with combinations of metallic gold, green, copper and silver, while related species can show dramatically different colour patterns. The University of Nebraska's scarab database, for example, records Chrysina optima from Panama and illustrates a gold colour variant. Chrysina chrysargyrea has also been recorded from Chiriquí, with photographs showing different colour forms, including a red variant.
This variation makes identification surprisingly difficult.
Two beetles can look broadly similar to somebody walking through the forest but turn out to be different species. Conversely, individuals belonging to the same species can sometimes have strikingly different appearances.
That is one reason entomologists don't identify these beetles simply by looking at a photograph and saying, "That's a gold beetle."
They may need to examine extremely small morphological characteristics, geographical distribution and, increasingly, genetic information.
Scientists are still discovering new species
Perhaps the most exciting thing about Panama's jewel scarabs is that the scientific story is far from finished.
In one example, researchers described Chrysina kalinini as a new species from Panama. Its identification was based not only on physical characteristics but also on mitochondrial DNA, specifically the COX I molecular marker. The new species was closely related to Chrysina resplendens, but the combination of morphology and molecular evidence supported its recognition as a distinct species.
This is modern taxonomy in action.
For centuries, scientists primarily compared physical characteristics. Today, they can also compare DNA. That means an insect that looks almost identical to another species may turn out to have a very different evolutionary history.
And Panama is an especially exciting place for this kind of research because its geography brings together species associated with Central America while also forming a biological bridge toward South America.
Panama's mountains are especially interesting
The country's incredible elevation changes are another reason its beetle fauna is so diverse.
Panama rises from coastal lowlands into mountain systems with cooler and wetter forests. Places such as Chiriquí and other highland areas provide very different environments from the hot tropical forests around the Caribbean and Pacific coasts.
Some Chrysina species have relatively restricted distributions. Chrysina optima, for example, has been recorded in Panama's Chiriquí Province as well as Costa Rica. Chrysina chrysargyrea has also been documented in Chiriquí.
This means that finding one of these beetles can sometimes tell an entomologist something about the particular environment where it was discovered.
A beetle crawling across a leaf is therefore more than just a pretty insect. It can be a tiny piece of information about geography, evolution and the history of Central American forests.
They belong to the scarab family
Despite their jewel-like appearance, these beetles are fundamentally scarabs.
The genus Chrysina belongs to the family Scarabaeidae, subfamily Rutelinae, tribe Rutelini. They are often called jewel scarabs because of their spectacular metallic appearance.
The scarab family is enormous and contains insects with wildly different lifestyles. Some scarabs are associated with dung, some with decaying organic material, some with plants and roots, while others are predators or fungivores. A large review of Panamanian scarabaeoid beetles emphasizes just how diverse the ecological roles of scarabs can be.
So the fact that a beetle looks like jewellery tells you surprisingly little about what it actually does in the forest.
There is an incredible story hidden underneath the beetle
The adult golden beetle that you see crawling through the forest represents only one stage of its life.
Like other beetles, Chrysina undergoes complete metamorphosis. The animal begins life as a larva before eventually transforming into the spectacular adult form. That means the shiny little creature wandering across a leaf has gone through an entirely different body form earlier in its life.
This is one of the great recurring themes of tropical biology. The rainforest isn't just filled with colourful adult animals. It contains enormous numbers of organisms moving through completely different stages of development, many of which are rarely noticed by humans.
The brilliant adult beetle is essentially the final, highly specialized chapter of a much longer biological story.
The golden beetle at night
If you spend enough time in a Panamanian rainforest, you eventually learn that daytime and nighttime have almost completely different insect populations.
At night, artificial lights can attract insects from the surrounding forest, which is one reason scientists have historically used light traps to study tropical insects. Beetles that seem almost impossible to find during the day can suddenly appear around lights after dark.
This is one reason that a rainforest night walk can feel like entering a completely different ecosystem.
Instead of looking for monkeys in the trees, you are suddenly looking at moths, katydids, beetles, spiders, crickets, praying mantises and other creatures that become active after sunset.
And occasionally, among all the strange insects, you find something that looks as though somebody dropped a gold coin onto a leaf.
Why scientists care about these beetles
The scientific value of Chrysina goes far beyond identifying pretty insects.
These beetles provide researchers with opportunities to study evolution, biogeography, genetics, sexual differences, species formation and structural colour. The recent Panamanian revision was not simply a catalogue of pretty beetles. It involved examining diagnostic characteristics, distribution maps, taxonomic relationships and specimens from collections.
And because researchers continue to discover new populations, new country records and even new species, these beetles demonstrate how incomplete our understanding of tropical biodiversity still is.
There is something wonderfully humbling about that.
You can walk through a forest that has been visited by scientists for generations and still encounter an insect that represents a gap in our knowledge.
Panama's tiny pieces of jewellery
Perhaps the best way to appreciate Panama's golden beetles is to stop thinking of them as simply beautiful bugs.
They are tiny examples of evolutionary engineering.
Their metallic appearance is produced through structures far smaller than the eye can see. Their colours vary between species and sometimes within species. Their distributions can be remarkably localized. Their evolutionary relationships can be investigated using DNA. Some species have only recently been documented in Panama, while others have disappeared from scientific collections for generations before being rediscovered.
And that is what makes encountering one in the Panamanian jungle so special.
You are not just looking at a shiny beetle.
You are looking at a living optical device, a product of millions of years of evolution, and potentially one small piece of a biodiversity puzzle that scientists are still putting together.
In a place like Panama, where the forest is full of creatures that most visitors never notice, sometimes the most spectacular wildlife isn't a monkey, a sloth or a toucan.
Sometimes it is a tiny golden scarab crawling quietly across a leaf, reflecting the rainforest sunlight like a microscopic piece of treasure.