a bioluminescent beetle
A bioluminescent beetle. Image: Pablo Bombín, CCO, via iNaturalist

Brazil is bursting with bioluminescent insect species.  

Bioluminescent insects produce light using a chemical reaction. In scientific terminology, an enzyme called luciferase oxidizes a compound called luciferin, and that creates the light.  

Fireflies may be the best known group of bioluminescent insects. Scientists have identified around 350 firefly species in Brazil, and experts think that there are many more species to be found there. Fireflies are actually a family of beetles called the Lampyridae.

Firefly larvae of the Psilocladus genus. Image courtesy of André Alves

There are other families of bioluminescent beetles in Brazil too. Click beetles (Family Elateridae) and railroad worms (Family Phengodidae) are bioluminescent sights present in many ecosystems.  

The Cerrado is a savanna-like ecosystem in central-west Brazil. In the Cerrado, the larvae of the click beetle Pyrearinus termitilluminans create a unique spectacle. The larvae hide on large termite mounds and emit light to attract prey. Their bioluminescence lights up the mounds’ silhouettes with bright green dots. 

Bioluminescent larvae glowing in termite mounds to attract prey at Emas National Park. Light pollution from Chapadão do Céu can be seen in the background. Image courtesy of Vadim Viviani

Vadim Viviani says that this breathtaking sight is now becoming rare. He is a professor at the Federal University of São Carlos, and an expert in bioluminescence. “In the 1990s, we would see many of these termite mounds full of fireflies and other bioluminescent insects, even in areas of pasture,” Professor Viviani said. “Now, sugar cane is grown in most of the areas and we hardly see any.”

Professor Viviani found that bioluminescent beetles are declining in the Cerrado. He is part of a team of researchers that surveyed different areas of the Cerrado for bioluminescent beetles. Over the last 30 years, the researchers recorded 51 species of bioluminescent beetles across all the study areas. They found that over that time that many of these species declined in the Cerrado. 

For example, the scientists found signs of declining populations of railroad worm beetles. Before 1996, scientists recorded an average of 10 beetles every surveyed night, belonging to nine different species. In 2005, they saw only around three railroad worms a night, of two different species. After 2008, despite 12 nights of effort, the scientists didn’t find a single railroad worm.

An adult firefly of the Photinus genus. Image courtesy of André Alves

Pesticide use and habitat loss (change from natural habitat to soy and sugar cane crops) caused some of the observed decline of bioluminescent beetles in the Cerrado. However, this wasn’t the only problem uncovered by research team. The team discovered evidence that artificial light at night (light pollution) affects adult railroad worms.

The impact of light pollution seen from Serra dos Órgãos National Park, Teresópolis, Rio de Janeiro. Image courtesy of André Alves

Stephanie Vaz explains why artificial light is harmful to bioluminescent beetles: “Light affects these bioluminescent animals through competition. Males and females that rely on a luminous signal to find each other can be rendered basically blind. Larvae that need their light for self-defense or to attract prey can also be affected.”  Stephanie Vaz is a  firefly researcher at the Federal University of Rio de Janeiro.  

The small glow of tiny bioluminescent animals is no match for a halogen lamp or the light pollution coming from nearby cities.

“The increasing levels of artificial light coming from nearby urban centers at night may threaten several bioluminescent species inside Emas National Park [a protected area of the Cerrado],” says Professor Viviani. “The problem merits special attention and further studies.”

David Brown adapted this story for Mongabay Kids. It is based on an article by Bernardo Araujo, published on Mongabay.com: