Insects of a Lost World

The Cretaceous period was the final and longest period of the Mesozoic Era. For insects, it was transformative. The rise of flowering plants (angiosperms) created entirely new ecological relationships, amber deposits preserved insects in extraordinary three-dimensional detail, and many modern insect families either originated or diversified during this time. The Cretaceous ended with the K-Pg extinction event 66 million years ago, which killed the non-avian dinosaurs but left most insect lineages intact.

The Rise of Flowering Plants

The most important development for insects during the Cretaceous was the rapid diversification of flowering plants (angiosperms), beginning in the Early Cretaceous and accelerating through the Late Cretaceous. Before this, the plant world was dominated by conifers, ferns, and cycads. Angiosperms introduced new food sources — nectar, pollen, fruit — and created new habitats. Insects responded with explosive diversification, as detailed in Insect-Plant Co-Evolution.

Bees appear in the Cretaceous fossil record for the first time, likely evolving from wasp ancestors in response to the availability of angiosperm pollen and nectar. Early bees are preserved in Burmese amber, dating to approximately 100 million years ago. Butterflies and moths (Lepidoptera) also diversified significantly, with some of the earliest definitive Lepidoptera fossils dating to the Cretaceous.

Amber Preservation

Some of the most spectacular Cretaceous insect fossils come from amber — fossilized tree resin that trapped insects and preserved them in three-dimensional detail, sometimes including internal tissues, color patterns, and even parasites. Major amber deposits of Cretaceous age include Burmese amber (~99 million years old), Lebanese amber (~130 million years old, among the oldest insect-bearing amber known), and deposits in France, Spain, and Canada. See Amber as a Time Capsule for more on amber preservation.

Amber from the Cretaceous has revealed an astonishing diversity of insects, including ants, wasps, beetles, flies, termites, thrips, and many other groups. Many of these look surprisingly similar to their modern relatives, demonstrating that many insect body plans were already well established by the mid-Cretaceous.

The First Ants

Sphecomyrma, described from Cretaceous amber found in New Jersey, is one of the most famous "missing link" fossils in entomology. It combines features of wasps (from which ants evolved) with features of modern ants, providing direct evidence for the wasp-to-ant evolutionary transition. By the Late Cretaceous, ants were already diversifying, though they did not reach their modern ecological dominance until the Cenozoic.

Other Cretaceous Insect Groups

Termites diversified significantly during the Cretaceous, developing eusocial colony structures. Scale insects, aphids, and other plant-feeding hemipterans radiated alongside flowering plants. Parasitoid wasps continued their diversification, evolving alongside new hosts. The overall picture is of insect diversity approaching modern levels, driven largely by the explosive diversification of angiosperms.

The K-Pg Extinction

The asteroid impact at the end of the Cretaceous (66 million years ago) caused a mass extinction that ended the non-avian dinosaurs and many other groups. Its effect on insects, however, was comparatively mild. While some insect lineages suffered losses — particularly those dependent on specific plant hosts that went extinct — most major insect orders survived the boundary. The insect fossil record shows decreased diversity in the immediate aftermath, followed by a relatively rapid recovery in the early Cenozoic.

This resilience is thought to be due to insects' small body size, fast generation times, and ability to enter dormancy. Many insect lineages that survived the K-Pg event went on to dominate the Cenozoic world, giving rise to the modern insect fauna we see today. For more on how insects weathered extinction events, see Mass Extinctions and Insects.