A swarm of prehistoric insects fossilized in amber is showing scientists just how vibrantly colored the world was 99 million years ago.

Fine structural detail necessary for the conservation of color is rarely preserved in fossil records, making most reconstructions based on artists’ imagination.

However, a research team at the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS) has now unlocked the secrets of true coloration in 99-million-year-old insects.

“We have seen thousands of amber fossils but the preservation of color in these specimens is extraordinary,” said Huang Diying from NIGPAS who is a co-author of the study.

One of the reasons it’s so hard for scientists to tell the colours of prehistoric creatures is due to what’s left from them – a fossilised bone can’t convey what colour the animal was. But this time, using Burmese amber they managed to peer into the world of ancient colours.

Scientists have been able to unlock the secret behind the vibrant colors of prehistoric insects using these 99-million-year-old specimens. (Cai et al., PRSB, 2020)

Amber is essentially resin produced by ancient coniferous trees that grew in a tropical rainforest environment. Animals and plants trapped in the thick resin got preserved, some with life-like fidelity.

The researhers analyzed 35 amber specimens found in an amber mine in northern Myanmar that date back to “the golden age of dinosaurs” in the mid-Cretaceous period some 99 million years ago. The team was on the lookout for specimens that possessed intense structural colors. Structural colors are colors that make peacock feathers and butterfly scales appear iridescent; in this case, they were created by the outer cuticle of the insect’s exoskeleton.

The rare set of amber fossils mainly includes cuckoo wasps and chalcid wasps with metallic bluish-green, yellowish-green, purplish-blue or green colors on the head, thorax, abdomen, and legs.

Interestingly enough, the cuckoo wasps in amber (see, for example, the first green insect in the series of images above) were nearly the same colour as the cuckoo wasps that are around today.

A modern cuckoo wasp. Credit: Wasrts/Wikimedia/CC BY 4.0

But why did these bugs have more vibrant coloring than other specimens found in amber? To answer this question, the researchers used diamond knife blades to cut through the exoskeleton of two of the wasps and a sample of normal dull cuticle from an amber specimen not part of the colorful batch.

By using electron microscopy, the scientists found that in the dull-looking specimen the nanostructures which create the structural colours were badly damaged, which explains their mostly brown and black coloration.

The exoskeletons on these colorful insects (left) have remained intact because of the tree resin that encapsulates them. (Cai et al., PRSB, 2020)

The nanostructures on the colorful amber specimens, however, were perfectly intact, which explained why they remained so colorful even after 99 million years. These findings suggest that the vibrant coloring seen now on these prehistoric bugs was likely how they looked when they were alive

While such discoveries are definitely fascinating, it’s important to note the palaeontology community is currently debating whether the scientific information that can be gleaned from these specimens collected and sold in Myanmar is worth the price of the potential human consequences, including the persecution of the Kachin ethnic minority. Amber has driven remarkable discoveries about the prehistoric world, but concerns about its sourcing are growing.