Meganeura was an insect with a wingspan of about 70 cm that hunted over what is now central France about 300 million years ago, late in the Carboniferous. It is often called a giant dragonfly, but it was a griffinfly, from an extinct order only distantly related to dragonflies. It is one of the largest flying insects ever found, and its size lies at the centre of a long argument about how insects could once grow so large, an argument that a 2026 study has reopened.
A griffinfly, not a dragonfly
Griffinflies, formally Meganisoptera, looked enough like dragonflies to be named Protodonata at first. In 2005 Grimaldi and Engel proposed “griffenfly”, now often spelled griffinfly, because the two groups are so far apart. The differences show in the wings. Griffinflies had no pterostigma, the thickened patch of cells that stands out near a dragonfly’s wingtip, and they had a simpler pattern of veins and no nodal flexion structures. In Meganeura the thorax and abdomen were about equally thick, unlike the slim abdomen of a modern dragonfly.
The fossils come from the coal mines of Commentry, where they were first found in 1880. The mining engineer Fayol passed giant insects to Brongniart, who in 1884 named a four-winged specimen Dictyoneura monyi after Mony, the recently deceased manager of the mines. A year later he gave it its own genus, Meganeura, meaning “large vein”. In 1943 Carpenter showed that half of Brongniart’s six specimens were counterparts of the other half, leaving three individuals in his collection. Its overall anatomy is still poorly known, so much of the detail comes from close relatives.
The size, checked
The wingspan is well agreed. Published figures run from about 65 to 75 cm: Nel and colleagues give about 700 mm, Garrouste and Nel 70 cm, and an estimate by Tillyard from 1917 gives 680 mm. A single wing reached 32 cm. For comparison, the largest dragonfly alive today does not exceed about 20 cm. Meganeura may not hold the record outright, because Meganeuropsis permiana, from the early Permian of Kansas, had a wing of 330 mm and a wingspan of up to 710 mm.
The rest is less secure. Garrouste and Nel give a body almost 40 cm long, while Wikipedia gives up to 60 to 75 cm, nearly the wingspan. Meganeuropsis, about the same width across the wings, was almost 43 cm long, which fits the lower figure. Estimates of mass are further apart: 17.8 g from May in 1982, who thought it might be too low, about 60 g from Paul in 2002, and 100 to 150 g from Cannell in 2018.
A hawker in open air
Much of what is known about how it lived comes from Meganeurites gracilipes, a relative from the same beds at Commentry. Nel and colleagues found enlarged compound eyes that met along the midline for much of their length, strong jaws with sharp teeth, and strong spines on the lower legs and feet; thorax and legs together worked as a “flying trap”. They concluded that these insects were hawkers, patrolling above rivers, lakes, open forest or even the canopy, because such long wings would have been a handicap among dense trees. The food was mainly other insects.
They were not agile fliers by modern standards. Without nodal flexion structures they probably could not make the abrupt turns of a dragonfly, and like other early groups they could not fold their wings back over the abdomen. Cannell suggested a wingbeat of about 3 per second, against 18 for the largest living dragonfly, with short bursts of flight and much time spent perching.
The oxygen question
In 1911 Harlé proposed that Meganeura could fly only because the air then held more oxygen than today’s 20 per cent. The idea has since found some support, but it has a stubborn problem: griffinflies with a wingspan of 45 cm lived in the late Permian of Lodève, France, when oxygen had already fallen.
In 2026 Snelling and colleagues reported in Nature that tracheoles, the fine air tubes in flight muscle, fill only about 1 per cent of the muscle or less in most insects, and concluded that oxygen supply there does not limit size. Some scientists reply that oxygen flow elsewhere in the body might still matter. Other explanations include the lack of flying vertebrate predators, proposed by Bechly in 2004, and the mechanical limits of the exoskeleton. The question remains open.
