Ancient Cockroach Unveiled

Russell Garwood, from ESE, has gone out of his way to explore a long lost world where cockroach-like insects grew up to 9 cm in size in order to understand just how these insects came to be so widespread.

It is the chef's worst nightmare, to open the cupboard door and find cockroaches scurrying away through impossibly small cracks. Cockroaches exist almost everywhere we humans leave waste unattended, and are guaranteed to put even the strongest stomach of it's food. Whilst most people try to avoid close encounters of the cockroach kind, Russell Garwood, from the department of Earth Science and Engineering, has gone out of his way to explore a long lost world where cockroach-like insects grew up to 9 cm in size in order to understand just how these insects came to be so widespread.

In a paper published in the journal of Biology Letters, Garwood, together with Mark Sutton of ESE, present the results of a new study of the early ancestors of cockroaches that lived around 300 million years ago in the Carboniferous period. The research presents a comprehensive 3D model of a fossilised specimen called Archimylacris eggintoni, which is an ancient ancestor of modern cockroaches, mantises and termites, in order to glean insights into its survival tactics.

The lead author of the study, Russell Garwood, a PhD student ESE, says, "The Carboniferous period is sometimes referred to as the age of the cockroach because fossils of Archimylacris eggintoni and its relatives are amongst the most common insects from this time period. They are found all over the world. People joke about it being impossible to kill cockroaches and our 3D model almost brings this one back to life. Thanks to our 3D modelling process, we can see how Archimylacris eggintoni's limbs were well adapted for all terrains, as it was not only adept in the air but also very agile on the ground."

The researchers created their images using a CT scanning device, based at the Natural History Museum in London, which enabled them to take 3142 x-rays of the fossil and compile the images into an accurate 3D model, creating a 'virtual fossil' of the creature, using specially designed computer software. The scientists used the models to visualise the Archimylacris eggintoni's legs, antennae, mouth parts and body, in unprecedented detail.

Scientists had previously known that Archimylacris eggintoni had wings, which suggested the bug could fly. However, very few limbs of this species - or other roach-like insects from this era - have been preserved in fossils.

In the new study, the researchers' model reveals that Archimylacris eggintoni had sticky structures on its legs called euplantulae. The researchers believe the euplantulae enabled Archimylacris eggintoni to stick to smooth surfaces such as leaves as they climbed across them, which may have helped them to lay their eggs above the ground in safer locations away from predators.

In addition, the scientists also discovered that Archimylacris eggintoni had claws at the base of its legs, which helped it to climb rough surfaces like trees, so that it could perch above the forest floor for safety or find alternate sources of food higher up.

The 3D model also reveals how Archimylacris eggintoni's legs could help it to run fast. The team noted that the legs were at a low angle to the body and fairly long, which they believe helped it to move quickly even when the terrain was difficult or uneven.

The scientists also reveal Archimylacris eggintoni's mouthparts, called mandibles, which helped it to grind up its food. The team say the mandibles are similar in appearance to modern day cockroach mandibles, suggesting they ate similar food, munching on decaying leaf and insect matter as it scurried from place to place.

Garwood adds, "We now think this ancient ancestor of the cockroach spent most of the day on the forest floor, living in and eating lots of rotting plant and insect matter, which was probably the bug equivalent of heaven. We think it could have used its speed to evade predators and its climbing abilities to scale trees and lay eggs on leaves, much in the same way that modern forest cockroaches do today."

In the future, the researchers will use their computer modelling technique to study other fossilised creatures from the Carboniferous period. They plan to learn more about spider-like creatures called the harvestmen and another species called Camptophyllia, which has yet to be classified by scientists.

Associated Personnel 

• Russell Garwood
• Mark Sutton