Mass Extinctions and Insects
Earth has experienced five major mass extinction events over the past 500 million years. Each affected insects to varying degrees, but insects as a group have proven remarkably resilient compared to many other animal lineages. Understanding how insects fared during these events reveals much about the factors that make species vulnerable or resilient to ecological catastrophe.
The Big Five
Late Ordovician (~445 Ma)
This extinction primarily affected marine life. Insects had either not yet evolved or were in their earliest stages, so the impact on insect evolution was minimal or nonexistent.
Late Devonian (~375–360 Ma)
Again primarily a marine event. Insects existed during the Late Devonian but were still in early stages of diversification. The effect on insects is difficult to assess given the sparse Devonian insect fossil record.
Permian-Triassic (~252 Ma, the "Great Dying")
This was the worst extinction for insects. An estimated 60% of insect families went extinct, including entire orders: the Palaeodictyoptera, Megasecoptera, Diaphanopterodea, Caloneurodea, and Miomoptera. The Meganisoptera (giant griffinflies like Meganeura and Meganeuropsis) also went extinct. The causes — massive volcanism in Siberia leading to extreme global warming, ocean acidification, and habitat destruction — devastated terrestrial ecosystems including the forests that many insect groups depended on.
Recovery took 10-15 million years. The Triassic insect fauna was markedly different from the Permian one, with new groups (beetles, flies, early hymenopterans) filling the ecological roles of the extinct orders.
Triassic-Jurassic (~201 Ma)
This extinction was less severe for insects than the Great Dying. Some lineages were affected, but most major insect orders that had established themselves during the Triassic survived into the Jurassic. The Titanoptera went extinct around this time.
Cretaceous-Paleogene (~66 Ma, the K-Pg event)
The asteroid impact that killed the non-avian dinosaurs had a comparatively mild effect on insects. Most major orders survived, though there is evidence of reduced diversity in the immediate aftermath, particularly among species dependent on specific plant hosts that went extinct. Recovery was relatively rapid, and the early Cenozoic saw insect diversity rebound and eventually surpass pre-extinction levels (see Green River Formation).
Why Are Insects Resilient?
Several factors make insects relatively resistant to mass extinction: small body size (requiring fewer resources), fast generation times (allowing rapid evolutionary response), the ability to enter dormancy or diapause, dietary flexibility in many groups, and the sheer diversity of species (making it statistically likely that some will survive any given catastrophe). The evolution of complete metamorphosis may also help, as it allows different life stages to survive in different conditions.