An international research team has completed a 2-year project to map insect evolution, finding they originated at around the same time as the Earth's first plants some 480 million years ago.
That suggests it was plants and insects together that shaped the early ecosystems of the Earth, they say.
By the time dinosaurs evolved to rule the Earth, insects such as dragonflies, damselflies and many other insect species had been around for millions of years, researchers report in the journal Science.
The findings come from a research project known as 1KITE, or 1K Insect Transcription Evolution, in which an international team of researchers was assembled to create a database of transcriptomes -- all the genes expressed in an organism -- for 1,000 insect species.
The result is the first "roadmap" of insect evolution ever created, the researchers say.
"When you imagine a giant map of the evolution of life on Earth, insects are by far the largest part of the picture," says Michelle Trauwein of the California Institute of Sciences. "We have not had a very clear picture of how insects evolved -- from the origins of metamorphosis to which insects were first to fly."
The genetic "roadmap" showed insects developed wings for flight 400 million years ago at around the same time land plants began to grow significantly upwards to form the Earth's first forests.
Insects flew for almost 200 million years before any other animal evolved the ability to do so, the winged reptiles known as pterosaurs, the researchers said.
Although life on Earth originated in water, the first species to move onto land and into the air were insects, they explained.
"The biodiversity of insects is huge; they are the largest species group on the planet," researcher Jessica Ware of Rutgers University says. "Whatever people do, insects did it first. They waged war, they took slaves, they learned to work cooperatively, they flew, they farmed."
Before insects began to evolve on land they would have required the presence of food provided by the first somewhat primitive terrestrial plant species, the researchers said.
"Plants and insects co-evolved simultaneously, each shaping the other," says evolutionary biologist Karl Kjer of Rutgers University, one of the leaders of the study.
The very first insects likely evolved from a group of venomous crustaceans known as remipedia, they suggest.
"We have absolutely no clue of how the first terrestrial insects might have looked, but somehow they must have resembled an animal with crustacean and insect features," says Bernhard Misof of the Zoological Research Museum Alexander Koenig in Germany, another of the study's leaders.
