Wasps, bees, ants and relatives comprise the megadiverse insect order Hymenoptera, the third most speciose animal group on Earth, far surpassing the number of known vertebrate species. All the four most diverse orders of animals (beetles, butterflies, wasps, and true flies) belong to the group of insects with complete metamorphosis, i.e. having a dormant pupa, jointly known as Holometabola. Other holometabolans are lacewings, alderflies, dobsonflies, snakeflies, scorpionflies, fleas, and caddisflies. Hymenopterans are currently regarded as a very old lineage, which had been the first to separate from the holometabolan stem, the view supported by molecular evidence.
Eighty years ago the Russian entomologist Andrey Martynov—well known for naming the two major divisions of winged insects Palaeoptera and Neoptera, stressing the importance of the wing folding pattern for insect evolution—suggested that wasps had arisen from snakefly-like ancestors.
New fossils, which are 260–270 million years old, support his view, firmly attaching the wasp lineage to the lacewing (neuropteroid) branch of the holometabolan family tree and dating its origin no earlier than Late Permian. These fossils are the oldest known Megaloptera: alderfly-like Parasialidae, and a newly discovered closely related family Nanosialidae.