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Insects: the first animals to fly
fossils from c. 400 million years ago (debated); flying by c. 325 million· Organism or group· Animals
Strong evidenceGood evidence; dates or details still being refined.
Six-legged arthropods that probably lived on land by about 400 million years ago and, by about 325 million, became the first flying animals.
See it on the Life map →What happened
Insects descend from crustacean-like ancestors that moved onto land. The oldest possible insect fossil, Rhyniognatha, comes from Scotland's roughly 407-million-year-old Rhynie chert, though some researchers think it is a centipede. Molecular clocks put insect origins near 480 million years ago. Winged insects appear in rocks about 325 million years old, roughly 100 million years before pterosaurs, the next flyers. About a million insect species are named, with millions more unnamed.
Why it matters
Flight let insects escape predators, find mates and spread widely. They became Earth's most diverse animals, central to pollination, decomposition and food webs.
The evidence (fossils, genes, rocks)
Fossils from the Rhynie chert and Carboniferous coal beds, plus DNA family trees and molecular clocks, including a 2014 study of 1,478 genes.
Still debated
How wings evolved, from gill-like flaps, outgrowths of the back, or both, and why winged-insect fossils are missing before about 325 million years ago.
Inside this (1)
Connections (3)
▸Arthropods walk onto land included the ancestors of Insects: the first animals to flyStrong evidence
The connection
Arthropods moved onto land several separate times. Millipedes and arachnids were among the pioneers; another line, crustacean-like animals related to today's shrimp, became six-legged hexapods. Wingless hexapods such as springtails lived among plants by about 410 million years ago, and insects arose from this land-living branch.
When and how
Molecular clocks suggest the Ordovician, about 480 million years ago; the oldest fossils, early hexapods in the Rhynie chert, Scotland, are about 407 million years old.
How sure are we?
DNA shows insects nest within the crustaceans (together called Pancrustacea), and early hexapod fossils appear alongside other land arthropods.
Debates and open questions
Which crustaceans are insects' closest relatives (remipedes are a leading candidate) and exactly when their ancestors left the water.
▸Insects: the first animals to fly grew to record size as Giant insects (Meganeura)Well established
The connection
Late in the Carboniferous, some flying insects reached sizes never matched since. Meganeura, a dragonfly relative called a griffinfly, had wings spanning about 65–70 cm. A leading explanation is the oxygen-rich air of the time, which let insects' simple breathing tubes supply bigger bodies.
When and how
Coal-forest swamps about 305–299 million years ago; Meganeura fossils were found at Commentry, France, in 1880.
The evidence
Fossil wings from France and elsewhere, oxygen estimates from rock chemistry, and lab experiments in which some insects grew larger in high oxygen.
Debates and open questions
Oxygen may not be the whole story; the absence of flying vertebrate predators before pterosaurs and birds may also have allowed giants.
▸Insects: the first animals to fly later gave rise to BeesWell established
The connection
Bees are a branch of the wasps: descendants of predatory wasps that switched to feeding their young on pollen and nectar. That shift happened as flowering plants spread in the Cretaceous, some 300 million years after the first insects.
When and how
Cretaceous period, by about 100 million years ago; the oldest bee fossils are in Burmese amber about 100 million years old.
The evidence
Bee fossils in amber, plus DNA family trees placing bees within a group of hunting wasps; molecular clocks suggest an origin about 120 million years ago or earlier.
Debates and open questions
Exactly when bees originated, and whether they evolved alongside the earliest flowers or slightly later, is debated.