An ancient wasp fossil has shown that winning designs are sometimes best left alone.

Evolution has not altered the wasp in 34 million years, scientists discovered.

Three fossil specimens, the oldest examples of their species known, were discovered on the Isle of Wight in the 1920s but wrongly labelled as ants. A new study of the fossils, housed at the Natural History Museum in London, has now confirmed their true origins.

Steve Compton, from the University of Leeds, who led the research, said: "What makes this fossil fascinating is not just its age, but that it is so similar to the modern species.

"This means that the complex relationship that exists today between the fig wasps and their host trees developed more than 34 million years ago and has remained unchanged since then."

Fig wasps are highly specialised and attach themselves to individual tree species, which rely on them to spread their pollen.

Each of the 800 or so modern species of fig tree is pollinated by just one or two species of wasp that ignore other fig trees.

The wasps measure just 1.5 millimetres in length. They have body shapes designed to help gain access to flowers hidden out of sight within the green "fruits". Although figs are thought of as fruits they are technically synconia - closed plant structures containing large numbers of tiny flowers.

Modern fig wasps carry the pollen they collect in special pockets beneath their bodies.

Using advanced microscopy techniques, Dr Compton's team was able to identify pollen pockets on the wasp fossils, and even grains of fig pollen within them.

This showed that 34 million years ago the wasps were carrying out active pollination in the same way they do today.

Further evidence from analysis of the insect's ovipositor, or egg-laying organ, suggested that the wasp and its host fig tree had been evolving together for millions of years.

"Although we often think of the world as constantly changing, what this fossil gives us is an example of something remaining unchanged for tens of millions of years something which in biology we call 'stasis'," said Dr Compton.

The research is published online in the Royal Society journal Biology Letters.

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