Extinct insects: Data & facts (as of: 02/2024)
Out of nearly one million scientifically described insect species, the International Union for Conservation of Nature (IUCN) lists only 12,568 species; 60 of them are said to be extinct. Most insect species have not been adequately studied and assessed by the IUCN, so the actual number of extinct species is likely much higher. The reason for the insufficient data is certainly the difficulty in assessing the abundance of typically small insects – in contrast, assessing the conservation status of mammals or birds is much easier.
Furthermore, it is much more difficult to prove that a once widely distributed continental insect species has gone extinct, while it is easier to demonstrate extinction for species that were or are exclusively endemic to islands. It is indeed a major challenge to conclusively determine that certain animals no longer exist across an entire continent. For this reason, most of the insects considered extinct are island species, such as the leaf beetle species Semanopterus kingstoni from Lord Howe Island, which disappeared around 1979, the Stephens Island weevil, which went extinct in 1931, or the Saint Helena dragonfly and the Saint Helena earwig from the South Atlantic island of Saint Helena; both disappeared in the 1960s.
According to the IUCN Red List, most insect species have gone extinct in North America – with 38 out of the 60 species listed as extinct. These include many moths and bees from the Hawaiian Islands. At least 9 insect species have also gone extinct within Europe: for example, Perrin’s cave beetle in France in 1945 or Tobias’ caddisfly in Germany in 1938. The other extinct insects come from Oceania, South America, South or Southeast Asia (such as Ridley’s stick insect), or Africa (e.g., the Mauritius snout butterfly and Morant’s blue).
Loss of natural habitat as a crucial factor
Insects are indispensable for the biodiversity and ecological balance of our world. They play a key role in pollinating plants, decomposing organic matter, and serving as a food source for other animals. However, they are globally experiencing a dramatic decline. The reasons for the extinction of insects are diverse and often interconnected.
One of the main reasons for the decline in insect populations is the loss of their natural habitat, primarily due to human activities such as urban expansion, industrialization, agriculture, and forestry. Perhaps the most famous example is the Rocky Mountain locust, which once swarmed Nebraska, USA, in groups of 12.5 trillion individuals. Today, it is believed that habitat loss and the plowing and irrigation of farmland disrupted the natural life cycle of the locust species, causing the insects to stop reproducing and go extinct around 1902. The disappearance of Darwin’s rove beetle in Argentina and the Brazilian diving beetle also involved habitat loss.
Threat from introduced species
The destruction of vegetation by invasive species can lead to the extinction of plants on which insect species feed. An illustrative example of this is the introduction of rabbits to the subtropical Hawaiian island of Laysan. The rodents destroyed the entire vegetation on the island, which covers only four square kilometers, in a very short time. In doing so, they also annihilated the host and food plants of the Laysan noctuid moth, which became extinct in 1911, and was in turn the main food source of the Laysan millerbird, which also became extinct shortly thereafter. The flightless Koolau spur-winged long-legged fly of the Hawaiian island of Oahu fell victim to introduced big-headed ants in the early 20th century.
The Xerces blue butterfly from California is considered the first American butterfly to become extinct in 1941 or 1943 due to habitat loss caused by urbanization and destruction of its host plants. Also, the larvae of Sloan’s Urania from Jamaica could not develop due to the destroyed habitat and vegetation, leading to the species disappearing in the early 20th century. The accidental introduction of the chestnut blight fungus from Asia to America by the chestnut casebearer moth caused the populations of the American chestnut, the host plant of the moth species, to collapse.
Extinct insects as a result of pest control
Pest control plays a particularly critical role in insect extinction. The use of pesticides and fertilizers significantly contributes to the decline of insects due to their direct toxic effects on insects or their food sources. For example, the coconut or Levuana moth, which lived on the Fiji Islands and threatened the coconut harvest, was eradicated in 1925 due to a biological control program: a parasitic fly species was introduced, which not only reduced the Levuana moth population as planned but exterminated it.
The exact reason for the extinction of the Madeiran large white around 1977 is not clear, but habitat loss and the use of fertilizers likely contributed to its disappearance. Possibly, a virus or parasite introduced to the Portuguese island also led to the final extinction of the butterfly species.
Another factor contributing to the disappearance of insects is climate change: Altered weather conditions, such as increased temperatures and changed precipitation patterns, can directly influence the life cycles of insects. Droughts and wildfires, intensified by climate change, further destroy habitats and threaten the existence of many species.