Adult osmylids are small to moderately-sized net-winged insects, with wingspans ranging from 1.4 to 3 cm. Smaller members resemble typical green lacewings, and larger species resemble antlions. Many species, namely those of the type genusOsmylus, have spotted wings. The thin antennae are short. They have two compound eyes, as well as three ocelli in between. Adult osmylids, like green lacewings, have prothoracalglands which produce foul-smelling compounds used to deter would-be predators. Their larvae are superficially similar to those of spongillaflies. They have peculiar mouthparts which look like a thin forceps with the ends bending outwards. The body is elongated and slender and terminates in two extensible graspers bearing tiny hooks; these are used to aid in locomotion and to grasp prey. The larvae are associated with damp, mossy habitats and are amphibious. They hunt small invertebrate prey, from which they suck the body fluids with their mouthparts. The adults are diurnal or crepuscular weak-flying insects which mostly prey on small invertebrates, supplemented with some pollen. Eggs are deposited in damp places, usually near freshwater.
Systematics and taxonomy
The osmylids are rather nondescript as adults, but among the Neuroptera they were generally assigned to suborder Hemerobiiformia. The Sisyridae were formerly believed to be closely related, even a sister group. But as it seems they are well distinct, the presumed close relationship being mistaken due to their larvae's superficial similarity caused by convergent evolution. Later, the green lacewings were held to be the osmylids' closest living relatives; together with some prehistoric lineages the Chrysopidae form superfamily Chrysopoidea which was considered sister to the presently monotypicOsmyloidea. However, mitochondrial DNA data found the Osmylidae to be basal to these as well as to the Myrmeleontiformia. In other words, the osmylids may be the most ancient living lineage of Neuroptera. Fossils described in 2016 indicate they are of Jurassic or Early Cretaceous origin. Their relationships to the numerous incertae sedis groups of Mesozoic Neuroptera can now be reinvestigated with regard to this hypothesis. The two subfamilies Eidoporisminae and Porisminae each contain only a single species, Eidoporismus pulchellus and Porismus strigatus, respectively. Both are endemic to Australia. A basal extinct member not assignable to a subfamily, Protosmylus, has been found fossilized in middle EoceneBaltic amber. The genus Burmaleon was described from two fossils found in Cenomanian ageBurmese amber and referred to subfamily Gumillinae, implying an Early Cretaceous or earlier age for the crown group radiation.
