Brazilian diving beetle

“Giant of the Dytiscidae”

Until recently, the Brazilian diving beetle Megadytes ducalis was known only from a single male specimen, which, according to rumors, was discovered before 1882 at the bottom of a water-filled canoe in the Amazon region of Brazil. It is currently housed at the Natural History Museum in London. Perhaps because the Brazilian diving beetle, at 4.75 centimeters in length, is the largest known species in the diving beetle family (Dytiscidae), German entomologist Lars Hendrich and his colleagues took a closer look at the insect in 2019. In doing so, they discovered ten additional specimens in previously unexamined parts of the zoological collections in Paris. All were collected at the end of the 19th century.

While the first known specimen, the type specimen, did not have an exact location of discovery, the locations of the other ten beetles are clear. All data indicate that they were collected in the municipality of Condeúba in the south of the state of Bahia in northeastern Brazil.

The IUCN lists the Brazilian diving beetle as extinct, although the discovery of ten additional specimens with precise historical location data allows for the possibility of now specifically searching for the Brazilian diving beetle and potentially rediscovering it alive.

The ten diving beetles found in the Paris zoological collections were brought to Europe by the French naturalist and entomologist Pierre-Émile Gounelle, who conducted seven expeditions to the east and northeast of Brazil between 1884 and 1914. He collected numerous spiders, insects, and plants that were later incorporated into the collections of the Muséum National d’Histoire Naturelle.

Brazilian diving beetle – Fact sheet

Scientific name	Megadytes ducalis, Bifurcitus ducalis
Original range	Brazil
Date of extinction	unclear, end of the 19th century or later
Causes of extinction	unclear, possibly habitat loss, insect trade

Diminishing biodiversity in Brazil’s Cerrados

At the end of the 19th century, Condeúba (formerly Santo Antônio da Barra), located in the Cerrados, the savannas in southeastern Brazil, was a significant site for the insect trade. Villagers from this region captured insects – most notably the mole beetle (Hypocephalus armatus) – and sold their catches at weekly markets.

The unique climatic and environmental conditions in the Brazilian Cerrados, with high humidity and temporary swamps in the wet savanna and residual lakes and ponds in the dry season, suggest, according to Hendrich, that the Brazilian diving beetle’s rarity in collections is indicative of its limited distribution.

Over the past 50 years, biodiversity in the Cerrado region has been increasingly threatened by the expansion of agriculture. Initially, there was extensive grazing, and since the 1980s and 1990s, the cultivation of monocultures on former grazing lands has become prevalent. Furthermore, forests are being cleared to create eucalyptus and soy plantations.

Today, two-thirds of the Cerrado region has been significantly altered by human activities. There are large plantations for rice, soybeans, corn, and sugarcane; livestock farming is also common. Frequent fires set for charcoal production, the use of fertilizers for agriculture, and the construction of dams negatively impact the ecosystem. Only one percent of the total area of the Cerrado is protected as a nature reserve.

Brazilian diving beetle: Targeted search efforts possible

With the location data identified by Hendrich and his colleagues for the Brazilian diving beetle, there is now the possibility for a targeted search for the largest diving beetle in the world. Until recently, nothing was known about its distribution area and preferred habitat. It is possible that the Brazilian diving beetle, currently considered extinct, may soon be rediscovered alive.

If the Brazilian diving beetle still exists, its habitat is endangered by the expansion of land and livestock farming in the natural Cerrado savannas. It is also possible that the insect trade at the end of the 19th century already led to declining population numbers of this giant diving beetle.

Hendrich’s study highlights the significant role collections play in biodiversity conservation; this includes the Muséum National d’Histoire Naturelle in Paris, often regarded as the world’s most extensive archive for biodiversity.

In addition to the Brazilian diving beetle, several other diving beetles are considered extinct: the Mono Lake diving beetle, the New Caledonian diving beetle, the South American diving beetle, the New Guinea diving beetle, and Perrin’s cave beetle.