Insects represent the most diverse and abundant group of organisms on Earth, yet they are not immune to extinction. The vast majority of insect species that have ever lived are now gone, their disappearance spanning immense stretches of geological time and involving cataclysmic global events. The fossil record reveals groups that vanished due to shifts in planetary chemistry, while more recent records document species wiped out by localized pressures from human expansion. Understanding these lost species helps illustrate the mechanisms that drive biodiversity loss.
Ancient Giants and Evolutionary Dead Ends
The Paleozoic Era featured insects of extraordinary size, a phenomenon directly linked to the atmospheric conditions of the time. The giant predatory insect Meganeuropsis permiana, a relative of modern dragonflies, possessed a wingspan that could reach up to 75 centimeters, or nearly 30 inches. This immense size was made possible by the high concentration of oxygen in the atmosphere during the Carboniferous period, which peaked around 30 to 35 percent, compared to the current 21 percent.
Insects breathe using a passive tracheal system, a network of tubes that delivers oxygen directly to tissues without the aid of lungs or a circulatory system. This diffusion-based method inherently imposes an upper limit on body size, as the distance oxygen must travel increases disproportionately with volume. The oxygen-rich air of the Paleozoic lowered this physiological barrier, allowing the tracheal system to support a larger body mass.
The reign of these giants was brought to an end by two major environmental shifts. First, atmospheric oxygen levels began a long-term decline toward the end of the Permian period. As oxygen decreased, the passive respiratory system of these large insects became physiologically unsustainable, forcing a reduction in body size.
The second major blow was the Permian-Triassic extinction event, often called the “Great Dying,” which occurred approximately 252 million years ago. Triggered by massive volcanic eruptions in the Siberian Traps, this event caused a severe collapse of terrestrial ecosystems. Specialized insect groups, such as the Palaeodictyopteroids and xylophagous beetles, suffered massive losses, with eight or nine insect orders becoming extinct entirely.
Case Studies of Recent Disappearance
Insects lost in the modern era typically succumbed not to planetary cataclysms, but to localized, human-driven environmental changes. The Rocky Mountain locust (Melanoplus spretus) offers a stark example of a species that went from super-abundance to extinction in only a few decades. This insect was famous for forming swarms so large they blotted out the sun, with one 1875 swarm estimated to contain over 12.5 trillion individuals.
The species, however, had a highly vulnerable life cycle tied to a specific, small geographic range for breeding. While the swarms ranged across the Great Plains of the United States and Canada, the permanent breeding grounds were concentrated in a few thousand square miles of sandy river valleys near the base of the Rocky Mountains. Settlers began moving into these same fertile river valleys during the late 19th century, starting new agricultural projects.
The farmers inadvertently destroyed the locusts’ core habitat by plowing and irrigating the soil. This activity killed trillions of eggs laid just beneath the surface, eliminating the species’ reproductive potential. Despite the species’ overwhelming numbers, the concentrated destruction of its limited breeding habitat caused its population to plummet rapidly. The last confirmed sighting of a living Rocky Mountain locust was in 1902, making it a documented pest species driven to extinction.
Scientific Factors Driving Insect Extinction
Many insects share biological traits that make them particularly vulnerable to extinction pressures, regardless of the time period. One such factor is high specialization, or niche dependence, where a species relies upon a very narrow range of resources or conditions. Insects with specialized diets, such as those that feed on only one or two specific host plants, face an elevated risk.
This specialization makes them susceptible to co-extinction, where the loss or decline of one species leads directly to the loss of a dependent species. If a single host plant is destroyed by habitat loss or disease, the dependent insect species, such as a specialized herbivore or pollinator, cannot simply switch to another food source and will also disappear. The resulting uncoupling of species interactions is a powerful mechanism of biodiversity loss.
A small geographic range is another trait that dramatically increases extinction risk. Species confined to a single valley, island, or isolated patch of habitat are more susceptible to localized environmental disturbance, such as a severe weather event or the introduction of an invasive predator. Small populations also face greater challenges from stochastic events, which are random fluctuations in birth and death rates that can overwhelm a small group.
Insects also have limited ability to adapt to extremely rapid environmental changes, particularly shifts in chemistry or climate. Since many insects are ectotherms, their metabolism and development are highly sensitive to temperature fluctuations. Sudden changes in temperature or precipitation patterns can disrupt the timing of their life cycles, such as emergence from pupation, causing them to miss the brief window when their host plant or mate is available.