What Is the Rarest Moth in the World?

Moths are a vast and diverse group of insects, with a wide range of sizes, colors, and behaviors. The concept of rarity is complex, as many species are naturally elusive or inhabit remote locations. Determining the absolute “rarest” is a challenge, but the story often leads to species pushed to the brink of extinction by environmental changes.

Sloane’s Urania: A Lost Beauty

The moth most often cited for its rarity is Urania sloanus, or Sloane’s Urania, a species now considered extinct. Native to Jamaica, this large moth was a day-flying insect known for its spectacular appearance. Its wings were iridescent, shimmering with metallic green, blue, red, and gold streaks on a black background, a result of light refracting through microscopic scales.

Historical accounts describe them swarming avocado tree flowers from sunrise until the afternoon heat. The last confirmed sightings date to the late 1890s, and the species is believed to have vanished by the early 20th century. Today, specimens are confined to antique collections, a silent testament to a lost piece of natural history.

The Path to Extinction

The disappearance of Sloane’s Urania illustrates co-extinction, where one species’ fate is tied to another. The moth’s life cycle was dependent on a specific food source for its caterpillars, which fed exclusively on the leaves of two toxic vine species in the Omphalea genus. This diet made both the caterpillars and adult moths toxic, with their bright colors serving as a warning to predators.

The primary driver of its extinction was the widespread clearing of Jamaica’s lowland rainforests for agriculture during the 19th century. As these forests were cut down, the Omphalea vines the caterpillars needed were destroyed. Without this singular food source, the moth population could not sustain itself. The loss of the lowland host plants proved catastrophic, breaking a link in the moth’s life cycle and leading to its decline.

Modern Contenders and Conservation

While Sloane’s Urania is gone, other moths face survival crises. In Australia, the Bogong Moth population has declined by over 99% and is now endangered. These migratory moths are a food source for the Mountain Pygmy-possum, so their decline has cascading ecosystem effects. A citizen science project, Moth Tracker, allows the public to report sightings to help researchers protect both species.

The Golden Sun Moth, also from Australia, is critically endangered. This day-flying moth has an adult lifespan of only one to four days and depends on specific native grasslands that are now highly fragmented. Conservation actions include identifying its remaining habitats and restricting development to protect the ecosystems where it survives. These efforts focus on habitat protection and public involvement to prevent other moths from sharing the fate of Sloane’s Urania.